I've seen a couple of Kimbo fights that made me wonder. Those bums either have no chin whatsoever (I'm talking wet toiler paper here), they aren't real professional fighters, or they are paid to take a dive
In big money fights I can't see it. For anybody getting the big money fights with Money May, Pacquaio or the Klitschkos the incentive to win is too great to be worth a one off payment for losing. Secondly they're most likely in with very little chance of winning anyway, so what's the point paying them to lose? It would be like paying me to lose a pro fight with any decent pro- I'm going to lose anyway
For most fighters in with a rising prospect (like an HBO hype job), I can see the case being made for them being paid to lose- but again, there is a big incentive for winning. The big money rematch, taking somebody's 0 on live TV watched by (potentially) millions, the chance to land a fight with an even bigger name, etc. Obviously there's a man's pride and integrity too
For a rising prospect or reigning champion to throw a fight- it's possible but the money would have to be pretty fucking big since a loss these days is far worse than a loss back in the day. I could see it happening if a fighter knows they have a career ending injury and can cash out this way, but there are still a load of reasons against it.
In small, untelevised fights- maybe. Who gives a fuck?