Most definitely have a small contract for signature by both parties. Once you develop a relationship it may loosen up a bit on signatures but always remember "not all realtors are created equal".
Years ago we had a broker contact us to do a clean out on a house where the owner had been dead for 5 days before being discovered. She was an extreme hoarder who had stacked items to the ceilings with a single path to the kitchen and bathroom. The basement had a sewage backup 8" deep and was full of clothes, mattresses and flies. Two dogs in cages died from lack of water.
I'm a big pro broker guy but we still put everything in writing, both paper and email. Broker requests we collect at closing. Contract was for payment at closing or 45 days, whichever was sooner.
47 days later no payment.
"Oh, she says, house hasn't sold and brother/executor lives out of state. Let me get back with you."
Day 49 I call. "Yeah, brother #2 is disputing the will so we're kind of in a holding pattern. Give me a day."
Day 52 I call. "Oh" she says "They didn't get a hold of you? They are wanting to work something out."
Lol I replied "Barbara, I don't know these people from a duck. I know you. You requested the work, you approved the bid, your name is on the invoice and you signed it." If I had to explain this to say a judge, or the board of realtors, as far as I know you own the house.
We got our check 4 days later.
All that said to reinforce that you don't leave your a employee in the office on day 1 with the safe open, and you don't work for new clients without a contract. Even a generic write up is better than expecting payment based on a verbal and nothing else. Hope that helps.