I have worked in IT sales for 25 years, and dealt with very senior executives at some of the UK's biggest co.'s. There is no doubt that loyalty and service are extremely important, but only if certain other commercial conditions are met; and only if that loyalty and service can't be obtained elsewhere at better terms. You should never feel bad about not buying from a dealer. It's up to them to persuade you they are worth spending money with. You are in charge of the relationship.
My advice would be for any major purchase:
Do as much research as possible on the products that you're interested in BEFORE you do any auditions. This puts you in a position of strength when the dealer is making claims about equipment and service. For example, this is especially true where the warranty is concerned. Just because a manufacturer offers a warranty of say, one year, doesn't mean under law they aren't liable for it for many years more for example. On this basis what looks like service, (i.e. where a dealer "persuades" the manufacturer to repair an item a few days after the warranty runs out) is actually your legal right. They are not doing you a favour or providing any kind of service. The issue of the warranties offered by co.'s was all over the papers recently. Often manufacturers themselves are ignorant of their legal obligations to the consumer.
Decide in advance what your personal terms and conditions are for buying equipment. Price? Service? A combination of the two? What does service mean to you?
There is nothing wrong with doing a demo and not buying from the dealer. It happens all the time and is an occupational hazard. The demo is an opportunity for the dealer to establish their credentials with you, not the other way round.
If you have thought through your personal terms and conditions prior to attending the demo, you can explain to the dealer what you're looking for in terms of service. You should explain that you will be demoing elsewhere. You can explain that price and service will be key and that you will be looking for three quotes etc. If you don't tell the dealer your expectations, how will you know if they will cover them for you? How will they know what they need to do to get your business if you don't tell them?
Even if you have a longstanding relationship with a dealer, don't take it for granted that they continue to give you the best prices and service. Benchmark them against others when you make a purchase and then take into account any previous service they have given you.
Just my 2p's worth.
AVI ADM9.1 - Logitech Squeezebox