Ah.. a little knowledge is a dangerous thing.
Try this one:
You: Which companies did we fail to sell to?
Sales: Acme Industries, OCP Corp, blah blah blah
You: Well.... why can't you just make a couple of more phonecalls?
The answer of course is sales isn't that simple. Neither is software development. Unless they really want hours of explanation in regards to architecture and maintenance I suggest they trust your judgement as a software developer.
This is the issue here, trust. You should explain to them they are displaying a lack of trust in your abilities by making these statements.
