TechRepublic has a good article on dealing with vendors who refuse to talk with consultants. I haven’t actually had any vendors refuse to talk to me, but I have had customers who have been bitten by making a bad call with a vendor.
Here’s my strong advice: If you have a consultant or computer support personnel, contract or employees, get them involved in all stages of purchasing any new hardware or software and listen to them.
I have designed custom software solutions, though I rarely do so any more. I’m well aware of how badly a custom project can go wrong. If the provider doesn’t feel like sucking it up and making your system work after you accepted delivery, life can become a nightmare.