Wow, some of you guys are so generous.
The main consideration is the amount of the bets. If someone on the sideline is making small sweat-bets then I don't see how a player would be expecting or hoping for anything. If the bets are more substantial, why wouldn't the side-bet winner want to throw the player 10-20%
or more jelly if they played good and won you money? Only good things can come from that. Ignoring the players while trying to make money off their work is where issues can arise.
Backing splits also depend on the amount of the bet. If someone pays my way to go play someone out of State, and covers lodging and other stuff and only wants to pay 30-40% if I win then that is good. They are putting up the money for the game and other stuff. Or if the bet is really big than 30-40% is good as well because the reward is there for the player. Aside from scenarios like that 50-50 after table fees is normal or 40% straight to the player regardless of fees is the low end.
It goes both ways. Why would players want to give up THEIR action to a backer who isn't going to take care of them? I don't care how broke I am, I am not going to play someone for $100 or $1000 knowing I am only going to clear 30-40% like some people are saying here. I am not going to risk losing my future action for a less than favorable split.
People like to think that most pool players are so broke and they are getting a free-shot with no risk. There IS risk in that the player is probably going to lose action if they win the match. Also, where is the backer going to be the next month or the next year when the opponent wants to come back and play an adjusted game? If the player gives up easy action to the backer and doesn't get a good split is the player going to be rewarded by getting backed in tougher games as well?
Backers can offer whatever they are willing to do but it all comes down to the relationship with the player. I want someone backing me who I trust and feel comfortable dealing with. I would assume that backers would want the same in a player. Favorable splits and voluntary jelly goes a long way in building relationships and partnerships in the poolroom.