It can be hard trying to write your own contracts, but with people today where everyone is an armchair lawyer, I can somewhat understand why they want to use an already existing contract instead of paying an actual lawyer to draft one up for them.
When I first started out as a business, I went online and looked at several contract types just to make sure I had the basic wording down. Eventually, I took a compiled copy, bits and pieces of several contracts, that were free to download and use without fear of plagiarism and had a contract lawyer look over it. It is actually not as expensive as one may think it is, only cost me $150 for the proofreading and to make sure that there were no open ends or liabilities through the use of some choice words, basically it is as bulletproof as it needs to be.
I would offer it up as a freebie, but as everyone’s business is slightly different and different states, counties and countries may render it as not as effective as it is for myself.
The only thing I can say is this. Describe your services and payment terms in plain easy to read language, don’t try to lawyer it up without a lawyer reading it. Those big words can sometimes put you in a situation that you don’t want to be in if you’re not careful.
There are several “free” online contract templates that you can edit, carefully and use freely. If they are just trying to copy yours word for word, they are just plain lazy.