Oh come on, car dealers are all the same.
I bought my Audi from a second-hand car dealer who insisted the extended 3-yr warranty I paid for was a "proper Audi one innit" (it's a good underwriter, but it's not Audi). And I'm in the process of getting a Golf from a main VW dealer and he's full of **** as well. They BS you from the moment they see you, and then let slip more things as you proceed with the purchase. There's a reason you need to keep your wits about you when you buy a second-hand car. Even from main dealers.
That's like saying if some one is knob head rest of us are? Not every one or every shop is out to screw you over, my Mrs has bought her last two cars used from a dealer and been zero issue, if op wants a refund then fine but I'd say least give them a chance to sort it before the whole you sold me a car unfit arquement and hassle that will ensue
Just re-read your edited post, yeah my focus was only on the fit for purpose bit.
