Most major universities in any country and every university in most advanced countries are up to spotting those who buy essays or even plagiarise by copying large chunks from books or borrow other people's works. Every essay goes through plagiarism software that can identify language, vocabulary, grammar and syntax that do not fit with a students known style.
I expect that any top university in any country is more than up to catching cheats. But many countries, although not the UK, have a wide range of establishments granting degrees and at the bottom are a number who by deliberate policy, money constraints or having poor quality lecturers cannot recognise or will accept (with a bribe) any essay a student cares to submit.
And as we know, in every country there are people who will buy degree certificates and the like. I seem to remember that Ian Paisley's doctorate, while not obtained dishonestly, was obtained from a small bible college somewhere in the mid USA, whose standards for a PhD, might be less stringent than in the UK.
Certainly there have been people in the public eye who have been found to have false qualifications purchased by responding to an advert.
