Sure I would, it is a standard method of retaining someone for services. Pretty much every time you hire someone's services it will involve a deposit, retainer, or payment up front. I just had work done on my trailer. I paid for the parts that needed to be shipped in before the work was done; paying the labour after the fact. I just hired a genealogist and paid a deposit on her services. You hire a lawyer and you pay a retainer. You pay for a month in advance for your lease or rent. You pay upfront a security deposit, and so on. Finally if one has shown a consistent failure to make payment, it is only fair the service provider is going to require payment upfront. This is how it works.