Mine is a different world because I play mostly in churches/congregations, however I did do the bar scene for about 15 years before.
Everyone knows the pitfalls of not having a contract, so lets deal with the problem of having one. It might keep you from playing at a place where they don't do contracts. The owner is insulted that you don't trust them.
In the first place, a contract is only as good as the word of the persons who sign it. Most of the people I deal with are trustworthy and I don't need one...but they appreciate that I took the time to write down the details in an "agreement" and treat this gig professionally anyway.
Unless you are a major draw that the venue can not do without, (and sometimes even if you are) the word "contract" causes mental images of lawyers and litigation. Who wants that?
If they act like it's uncomfortable to sign an agreement and mail it back, I just write them an email and say, "OK, to avoid misunderstandings and to make sure that we meet your expectations, I've written down what we talked about. Would you mind checking this out and let me know if I missed something?" It would include set up time, hotel room details, set length, address, contact info for everyone with cell numbers/email, how (check,cash, credit card?) and when payment would happen. Basically any details that would go in a contract.
Then follow up if they don't reply, to say "hey we really want to be sure that we got the details right, would you mind checking this out for errors and let me know if I got it right?
In other words it's not a legal "contract" per se but an agreement of the terms (which means a contract but not as intimidating). If they broke the contract, you wouldn't sue because the legal hassle and expense isn't worth it....but you have this email printed in your back pocket if they try to crawfish out of the deal you made with them. It's a way of showing them that you can prove they made an agreement.
I've never sued but it's probably as binding as a contract in a court room. Just the fact you can prove what the deal was is enough to keep it from going that far.
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It is what it is until it isn't