Sets are really hard to read, especially online, I think.

I've run into this situation many times. And generally, unless I can come up with a reasonable 2-pair hand that they would call a pre-flop raise with, I call or push all-in myself. If someone is lucky enough to catch a low set against my AA/KK I'm generally just going to have to pay them.

Usually, because you have raised pre-flop, there is enough money in the pot to enduce someone to make a play at it. If they are acting before you, people will oftentimes go all in on a semi-bluff or even middle pair hoping that you missed with Big or Miss Slick and they can just pick up the pot.

Remember, many books out there teach people that rag flops with no obvious draws are good ones to bluff / semi bluff at.

This bet can also be an overpair to the board but obviously still under your AA/KK. Othertimes it is the top pair with an Ace kicker. So there's a lot of hands that players will often go all in with here that you have beat.

Obviously, you have to worry about sets or 2-pair. But you still have outs for those, so even if you're behind you're going to outdraw sometimes. I'd say, in the end, unless I have a good read on the player, I call this bet.