There are a number of ways any professional writer can try to avoid dealing with a scamming client. However, to me, the most important strategy to avoid a scamming customer is to decide, right in the beginning, whether to work for someone or not.

Yes, it is the first few communications that can tell you about the seriousness of a client and whether they mean to pay you or not.
Generally, serious clients show the following characteristics (according to MY personal experience):
- They do a proper research about a writer before approaching them for their paper.
- They have a clear idea about why they are hiring you and why not other writers/companies.
- They are more concerned about the QUALITY of their work and practical guarantees for not being scammed.
- Once assured, they are ready to accept any method of payment that ensures the writer they will not scam him/her.
And some more.
On the other hand, a customer that is clever and thinks of getting away with the work without paying the writer shows the following characteristics:
- They are somehow hesitant in establishing a working relation with the writer.
- They try to drag the topic of payment on for some and place more stress on receiving completed research work.
- They want more and more work written as SAMPLE before they could decide they want to hire you or not.
And some more.
ANY serious writer would stop here!