That's just common sense for every purchase in life...........it's sad that people need a reminder. The contract holds both parties accountable.
I'm not a designer, but I have a very active clinic and consultation band business. I don't use a contract and have never had a problem. It's a side hustle so my living isn't dependent on that money,.
I never ask for money in advance. I prefer to "do work-get paid when best for the clients finance office"
This summer I had a school for whatever reason pay me before services were performed. I waited till after the session to cash the check.
I've never been cheated and I always strive to give more than expected.
I guess my point is for both sides to do what is expected if in a contract or just a spoken agreement.