How to protect my profit in Co wholesaling

[Venus Moshtagh]

Hi everyone, I am trying to do co-wholesaling but the problem is that most wholesalers don't accept to sign a contract with me when they even haven't opened the escrow yet. They have the property under the contract and that's it, they tell me: bring the buyer and if we sell the house will give you a fee, or say: add your fee to the purchase price and get it from the buyer. I feel something doesn't make sense. what if they don't pay me at the end? How can I keep track of which buyer they are going with? or how about if the buyer and them come to an agreement to split  my fee and not paying me ?  I am a newbie in this business and don't want to spend hours and hours behind the computer , finding buyers and not getting paid . I appreciate your advises , Thanks in advance