What Cross-Border Deals Get Wrong About Tax — and the Professionals Quietly Fixing It

By Ugo Aliogo

Somewhere in the mechanics of almost every major cross-border merger or acquisition, there is a moment when the spreadsheet stops making sense. The numbers that looked clean in the pitch deck turn out to carry embedded assumptions — about intercompany pricing, about the tax treatment of certain revenues, about the effective rates applicable to earnings in jurisdictions that the acquiring team has only a passing familiarity with. These moments are not unusual. In the world of international M&A, they are routine. What varies is whether the advisory team catches them in time.
Ajibola Oyeleye has spent much of his career in that gap — between what the financials appear to say and what they actually mean.
“Due diligence is fundamentally an act of translation. The numbers you’re looking at were produced by people in a specific context, under specific accounting conventions, reflecting specific commercial decisions. Your job is to understand that context well enough to ask whether those numbers would survive being read by someone with no interest in making them look good.”

It is a framing that cuts to the heart of why financial and tax due diligence in cross-border transactions is so technically demanding — and why the professionals who do it well tend to be those with unusual breadth of experience. Oyeleye holds credentials from three jurisdictions — CPA Canada, CIMA UK, and ICAN Nigeria — and has worked directly in tax and finance environments across West Africa, North America, and in collaboration with European counterparts. He has advised on transactions involving US-headquartered entities with worldwide operations, African commercial banks with multi-continental subsidiary structures, and multinational industrial and technology companies navigating regulatory frameworks that vary enormously across borders.
That breadth, he argues, is not incidental to the quality of his due diligence work. It is central to it.

“When you have only ever worked in one tax system, there are things you don’t know you don’t know. You have assumptions built into your analysis that you’ve never had to examine because they’ve always been correct in the environment you’re familiar with. Cross-border work breaks those assumptions. It forces you to see each jurisdiction on its own terms, rather than as a variation on something you already understand.”

The M&A landscape of 2023 was shaped by a set of pressures that made technically rigorous due diligence more important than it had been in many years. Interest rate increases had tightened deal financing conditions and raised the cost of errors in target valuation. At the same time, the OECD’s Pillar Two framework — with its global minimum tax of 15 percent — was beginning to reshape the tax planning assumptions underlying multinational structures in ways that had not yet been fully absorbed by the advisory market.

For professionals working at the intersection of tax and corporate finance, the implication was significant: deals that had been structured around tax efficiencies that Pillar Two would erode needed to be reappraised. And acquirers who had not done that reappraisal faced the risk of buying into a structure whose economics were already degrading.

“The single most common mistake I see in cross-border due diligence is that the tax analysis is backward-looking. It tells you what the effective rate has been. It doesn’t tell you what it will be. And in the current environment, that gap is enormous. The rules are changing. A structure that has been tax-efficient for a decade may not be in three years. If you’re paying for future earnings, you need to know what tax rate those earnings will actually bear.”
His approach to that problem draws on what he describes as a discipline of reading the policy intent behind legislation — not just the current statute, but the direction it is moving and the logic driving that movement.

“Tax reform doesn’t happen randomly. There is usually a coherent logic behind it — a theory about what the existing rules got wrong, and how the new ones will correct it. If you understand that logic, you can model future scenarios with much more confidence than if you’re just extrapolating from the current rules. It requires you to engage with tax policy as a subject in its own right, not just as a compliance framework.”

That engagement with tax policy at a conceptual level sets Oyeleye somewhat apart from practitioners whose focus remains primarily technical. It is a disposition he traces partly to his academic background — the Zoology degree that preceded his entry into professional finance — and partly to the breadth of his cross-jurisdictional experience.

“I studied biology before I studied tax. And one thing that biology teaches you is that systems evolve in response to pressure. Tax systems are the same. They evolve in response to the behavior of the entities they govern. Once you understand that dynamic — once you see tax law as a living system rather than a static code — you start to anticipate changes rather than just react to them. That’s a fundamentally different way of practicing.”

Beyond the technical dimensions of due diligence, Oyeleye has thought carefully about the interpersonal and communicative dimension of advisory work in high-stakes transactions — and about what distinguishes advisors who genuinely change outcomes from those who merely document them.

“There is a version of due diligence that is essentially a compliance exercise — you go through the checklist, you flag the risks, you write the report. And that has value. But the advisory work that actually makes a difference is the work that helps a client see something they wouldn’t have seen on their own. That requires a different kind of engagement. It requires you to understand not just the target company’s financials but the acquirer’s strategic logic — what they’re really trying to buy, and whether the structure in front of them delivers it.”

That strategic dimension has become more important as deal complexity has increased. In an environment where transactions routinely involve multiple jurisdictions, multiple tax regimes, and financing structures that interact with tax outcomes in non-obvious ways, the advisors who add the most value are those who can hold the full picture in mind simultaneously — and communicate clearly about what it means.

“In a complex deal, clarity is a professional skill in itself. There will always be more complexity than you can communicate in a single conversation. The question is: what does the client actually need to know to make a good decision? What is the one thing, if they don’t understand it, that will compromise everything else? Finding that thing — and explaining it in a way that a non-specialist can act on — is as important as any technical analysis.”

His career trajectory — from Lagos to Toronto, from compliance work to high-level M&A advisory, from a single jurisdiction to an international practice spanning three continents — reflects a deliberate expansion of exactly those capabilities. And it reflects, he says, a conviction about what kind of professional he wants to be.

“I don’t want to be the person who tells clients what already happened. I want to be the person who helps them understand what’s about to happen and what they can do about it. That’s a different ambition. It requires you to invest continuously — in understanding policy, in understanding markets, in understanding the industries your clients are in. You can never be done learning. The moment you think you have it figured out, the landscape shifts.”
He mentors junior CPAs outside his formal professional responsibilities — a commitment he describes as both a debt to the mentors who shaped his own trajectory and an investment in the quality of a profession he cares about.

“The things I know that are most useful to me now are not things I learned in any formal program. They are things I learned from watching excellent practitioners at work — seeing how they approached a problem, how they handled a difficult client conversation, how they decided what mattered and what didn’t. That transmission of craft from one generation to the next is how a profession stays sharp. It doesn’t happen automatically. Someone has to decide to do it.”
In a field where the pressures are intensifying and the technical demands are rising, the practitioners who combine that breadth of capability with that commitment to transmission are, arguably, the ones who matter most. They are not just doing the work — they are defining what the work can be.