Don’t interview the sales person.
If you do business with high tech companies, or other outsourcing companies, the salesperson is the worst person to talk to. They only care about scoring a sale, and will answer yes to all of your questions. If you talk to the technical manager, they might say no to all your questions, but at least that is honest.
In the long run, you will be dealing with project managers, staff members, and perhaps the boss himself. But, after the sale is made, the salesperson is out of the picture, so why deal with this person in the first place?
Sure, you are forced to deal with the salesperson, but you can ignore everything they say (recommended), and then have your second interview with a real person who gives real answers. You need to interview all members involved in your work if you choose to hire an outsourced company. If you can’t communicate with the programmers, or if the call center workers don’t communicate the way you like — you will be sorry — and the salesperson will not be in a position to help either.