This question is inspired by this extract from a question about minimum rating gain:
One of the top 10 players in the world (say Magnus Carlsen), wants to increase his rating to 3000. He has a good friend who has 1200 in rating, and who is willing to play a match of 200 games (2 each day for 100 days) against him. His friend will of course play his best, so this is by no means considered cheating.
According to https://wismuth.com/elo/calculator.html, Magnus will have way more than 99 % chance of winning a single game, but for simplicity, let's say he has 99 % chance of winning a game (which is an understatement). If we then forget about draws (for simplicity), Magnus would be expected a score of 198/200. That means a rating gain of 0.8*198 - 9.2*2 = 140 rating points.
Putting to one side, for the moment, the far fetched nature of the example, is there anything to stop this kind of behaviour?
I know two master level players who have achieved the 3 title norms they need for high level FIDE titles but are still about 150 points short of satisfying the rating requirement for the title. What stops them from following the suggestion and playing a 200 game match against a player rated 1000 points lower? Neither of them is getting any younger and the extra rating points they need seem to be getting harder and harder for them to gain.