Solid player opens from MP to 10, I call OTB with KQs, sb and bb call too.

9 high flop with a FD, checks around.
Turn Q, checks to me who bets 21, sb folds, BB calls, then solid player raises it to 50.

Am I at best chopping here? Am I ever ahead?

Probabaly not, you should be 3-betting this from the button time to time

you'll never know unless you call. i'd fold tho

consider 3betting

consider betting flop

fold turn

The first question you can ask yourself is what hands are ahead of me here that make sense: none by a solid player.

With a flush draw on the flop, AA, KK, QQ, JJ, TT, 99, A9s, smaller sets and flush draws should all be betting for value. On the turn all the same hands should be betting for value before it gets to you. Otherwise, we've misclassified this player as a solid player. I guess I could see AQs with the flush draw, but this is really passive play by a "solid player" to hope that you will bet for him on the turn unless you've been super aggro.

If we had more information, like that you've been super aggro, and the villain can expect you to try to take this away at some point, you could maybe see a slowed played 99, AA, KK or QQ, but again, with the flush draw on the flop, this is poor play as there can be scare cards on the turn that kill his action.

Have you seen this "solid player" bluff at all in the session? If not, I am inclined to believe he has misplayed this hand and was bailed out by your bet on the turn, but he is probably beating one pair hands.

If you have seen him bluff before, this could be a fancy play on his part with JT or a flush draw to try to use the BB against you, thinking that if he can make you fold he can probably get a fold from the BB too. Again, not very "solid" play as the bluff is too small and if you call he has to play a large bet on the river oop and possibly against two hands.

I'm concluding a fold is better than a call is better than a raise here, but I would reconsider whether the MP player is a "solid" player based on this play, unless you have more information that you're not sharing here about reads. Nothing that beats you was played correctly by the villain, and yet if you're ahead of a draw here, it is a very poor bluff by your opponent. I guess he might think a combo draw like JTs could be ahead of everyone, and he is actually value betting and hoping to hit on the river. I still think a big draw needs to bet more on the turn and probably bet the flop too.

Frankly, I think that villain needs to post here for advice more than you do.

What are stack sizes? This hand would benefit from a lot more information, specific suits and the other cards on the "9 high flop) may also make a difference. For instance, if the flop was 89x and the turn is Q, see how that makes a difference? Do we have a backdoor flush draw? You should have included more information. Poker is a game about analyzing all available information and making the best most well educated decision. You have left out 50% of the pertinent information. In general, if you are check-raised and have only top-pair good kicker you should likely fold. You could be faced with more significant action on the river (and have to play a guessing game again) and if the money goes in now, what are odds you are ahead, slim I would assume. Put some more effort into your post though and you will get better advice.

Yeah the other cards do make a difference. What hands has he been opening? Only Phil Helmuth top 10 hands, or, has he been raising JTs or other suited connectors? This looks like a combo draw to me who saw your weak bet and thought he could take it away.

Not 100% sure without stack sizes or the rest of the board though. If it is a dry board (other than a flush draw) I would say you are never good.

dude it would help if we actually new what the board was, this is really incomplete.

Difficult to imagine you getting raised this amount (looks like it wants action) by a hand you beat.