Hiring people to sell is dangerous. Effective salespeople are money-printing machines. If they didn't know that about themselves, they wouldn't be effective salespeople. So there is a serious adverse selection problem here: the most effective salespeople have their pick of who to work for. The hiring pool for salespeople is full of --- dominated by, probably --- salespeople who are much better at selling you on why you should keep paying them despite them closing no deals than on selling your customers anything.

You should learn how to "sell". That means a bunch of different things depending on how you decide to sell and is a basic business decision you should make early on. Make the decision such that your team can do the sales work. Hire sales when you have your process proven and nailed down.

37signals really got hiring right: you should (generally) hire a role after you've figured out how to do it yourself and doing it over and over again is becoming a material drag on the company.

If you feel like you need a deposit to start a project, don't do the project. In 14 years of consulting, including software development projects, I've never taken a prepayment. I can't remember a real problem I've had. I can, however, think of a lot of clients I've said "no" to because they didn't seem to have their shit together.