IT and Services both....
Operating model:
1) Brownnose the target's execs, and over free lunches and "fact finding" trips, tell them how skilled BigCo is, how much unbelievable talent it has at its fingertips, how much value it creates for its customers.
2) Tout 20% (that's the magic number) savings compared to the target's cost of tech/services. "That 20% mounts up year on year, but don't forget how much value we can create through our process expertise!". Knowing what 20% is doesn't need inside knowledge, the cost of every operation is well understood in the world of services and IT management. In reality there are no savings when BigCo do it - any target large enough to be of interest will have have its own economies of scale, a skilled workforce, competent IT, and functional management who understand full well that they're an overhead to be kept as low as possible. But target directors aren't bright enough to know this.
3) When the target invites bids, bid in at 25% below the anticipated in-house cost. Nobody will query the bid numbers, or the operating model. All the time, BigCo's capable and well rewarded sales and legal teams will be running rings around the target's beleaguered, outnumbered, out-experienced, and under-rewarded in house teams.
4) Target TUPE's across it's own team and processes, in return for a 5 year deal. For the first 14 months, other than teething troubles it all seems good. Up to this point, Big Co has been making a loss, because it's had the in house team, and been paying (the least possible) to whittle them down, and even when it's 100% offshore wage slaves, the inherent inefficiencies of offshore plus pretty high account management costs and bid costs mean their routine operating COST is near enough the same as the old in house team.
5) Now BigCo starts to progressively ramp the invoices - not just for the losses made to date, but because unlike the in house team, BigCo need to make a big fat 30% gross margin. This is normally achieved through things like non-standard service charges, and the inevitable changes that any corporate makes in a few years. So new divisions to serve (or not serve if disposed of), new processes, new laws or regulatory processes, new accounting standards - everything that the customer forgot to include, or couldn't specify, that's where the moolah is.
6) Four years in, the customer is paying 30% more than they were when they did it themselves. But by then all the senior management have swapped seats, the original business case and its assumptions is long, long forgotten, and there's no in-house team to say "Hold on! We're being ripped off!"
7) Target company directors pay themselves a big bonus, slap each other on the back in congratulation at what mega-business brains they are, because they've "simplified their processes", "engaged a world leading business partner", "got access to the unique skills/AI prowess of BigCo".
8) Target company investors wonder why costs have gone up. Target company employees wonder why the service has turned to shit.