It might be difficult for an SE to be available every time a salesperson wants them. In fact, the better an SE is, the more salespeople will lean on them, and also prefer them to other less successful SEs in the organisation.
The trick is, as a salesperson, sometimes it is an easy option to just get the techie in to show them the product. However, done too soon, this leads to giving an evaluation before finding that vital power person who could actually buy the product.
So obviously, a good SE skill is to have that power to lean back on the salesperson and get confirmation that the process has been followed up to that point. And then ask, is this necessary.
Although it is nice showing the product around, it doesn't always move the deal forwards, and if you show the wrong things, it can move things backwards!
Focus on PROOF. Prove that the product does what they need. No point in showing irrelevant things, just make sure they believe it works, and that it fits their vision (or redefines) of how they can solve the business problem.
Doing the right Proofs leads to moving the sales process forward, and removing any final doubts over whether this is a solution to the customer's problem.
Beware of people who just want to see the product, or think it is their job to evaluate fully every product under the sun. If you don't have any reason to think the customer could and will buy if the evaluation is succesful, then you shouldn't be in there.