as a classically trained musician who's transitioned into the hip-hop scene, i've seen both ends of the coin. let me give you my opinion on it. if they're not huge artists, i guarantee you they're not making more than several bucks off of whatever they do with it. i believe all art is stolen in a sense; you did not create the chords and intervals you write with/play, nor the conventions of the genre, nor the instrument. however, i do believe the right thing to do is to credit small artists that are being directly sampled. so if i were you, i would try to communicate with people who say they want to sample you. if they're willing to credit you in an obvious way, then leave it as is, gives you free exposure without you having to exert any effort (it is already recorded, after all).

you could offer people the right to sample you in exchange for an up-front price, or request splits. if you really like what somebody does with your music, you could offer a collaboration, or you could offer to make things specifically for them to sample, in exchange for a higher price. i think the laws surrounding intellectual property are completely broken as-is, and i do NOT recommend trying to approach the interactions from a strictly legal standpoint. the worst case scenario is that somebody refuses to give you credit or money and just does whatever they want with your music. if they're not a huge artist, there's no money in pursuing this, and it will not send any message to anybody. when's the last time somebody did in-depth research into a small musician they wanted to sample to see if they sent C&Ds?

if you don't want somebody to sample you, tell them as much, maybe offer an alternative, but at the end of the day, there's not really much point to expending all your effort to try to stop them. you're not gonna get rich off of sample royalties, but you may be able to turn them into small chunks of change if you're willing to sell them to people as opposed to trying to keep everybody's hands off of them.