Write "deposit (定金)" and not "booking money (订金)" when you take money, state the penalty amount, and review payment terms as if you were making a loan

In plain words

Only the word "定金" brings the double-return rule: if you break the contract, you don't get the money back, and if the other side breaks it, they must return double. The part above 20% of the contract amount doesn't count. If it is written as "订金," the law has no such rule. Giving payment terms is the same as lending your own money to the other side for nothing, and if they go under, it is a bad debt.