When you receive a proposal from email@example.com do you take it seriously? By not having a registered domain and paid email hosting is the sender smartly saving money so he can pass the savings on to you, or is it possible he just got into this business and is just reselling someone else’s stuff as quickly as he can from an anonymous email account he can close if the pressure gets turned up?
This is not to say no one with a gmail address can be a legitimate service provider, but it can certainly be a clue that the company in question warrants some deeper investigation into its history and depth. Particularly if the company in question is a technology provider ( for whom the registration of a business internet domain should be a simple matter).
When a company is set up just to sell a technology solution, but not equipped to support it, things can get hairy pretty fast. At Ripple we provide the technology solution, IT support, and consulting to keep things running smoothly.