In the movie, Beetlejuice talks about getting the Maitland's business, yet we never hear what he wanted from them
What did he expect for compensation?
While the Maitlands do wall upon Betelgeuse, they never reach an agreement.
Beetle Juice looks offended. BETELGEUSE Me, scary? You be the judge. ANGLE He swirls his face and shoulders into a horrifying image. Pleased, he laughs at himself. BARBARA (decisively) Honey. Let's go. ADAM Go? What d'ya mean? We need help. BARBARA No, we don't. We can work something out ourselves. We just have to try harder. BETELGEUSE Hold on. Let's not be squeamish, missy. You rang my bell, you gotta lick the pump. I'm rolling! BARBARA grabs Adam. Betelgeuse is getting mad. Not pretty. BETELGEUSE Folks, be reasonable here. I'm at your service. You be the judge. I'm a harmless guy. Try me. BARBARA Home. Home. Home! ZAP They are gone. Betelgeuse is furious. BETELGEUSE You fresh corpse creeps! Who do you think you are?... Walking away from a professional?
Essentially, the Maitlands are put off by Betelgeuse's manners and approach, hes self-advertising, and decide not to use his services.
Because of this, no contract is made, no agreement reached. We never learn what he would have requested in payment.
Later on in the movie we learn that if he gets married, he will no longer be stuck in either afterlife or the kind of limbo or purgatory they are in (it’s not clear). See this clip:
This is why he tries to marry Lydia. So it’s possible that his “business” as a “bio-exorcist” is part of his machinations to give him enough power in the real world to get married. It almost works.