I agree with you on this 100%.....I am this way with many things.
Once I find someone I like to deal with, that not only gives me good service but most importantly knows their stuff, then I don't go elsewhere.
Getting the knowledge of someone that knows their job/product so I make the right choice & then get my moneys worth out of my purchase is more important to me than a bit more discount(or free stuff) on the wrong purchase that may not be the best use of my money.
Had this happen recently to a mate buying a motorbike.
He thought he'd really got a bargain on a race bike. All he got was incorrect info/bad advice leading to a purchase that he wish he hadn't made.
Henry Ford