Or go with option 2: Ring doorbell, drop flaming bag of shit, run away.
Any agreement signed between 2 parties on paper is a contract. Even if it's on a napkin. Just write up something like "This is an agreement between X and X" then list what services/products they will get and what price they will pay. Have both parties sign and you will now be able to go after them in small claims court if they don't pay you. You have to pay filing fees and court costs but the judge will order the party that owes you $ to pay for that if you win.