I have found tons of attitude and arrogance at many of the gun shops I have been in. One guy sold me some pricey (as compared to surplus) non-steel core ammo and a few days later at the club he happens to be there and accuses me of shooting steel core ammo which is banned at the club - and I was shooting the ammo he sold me as non-steel core. and btw it is not steel core. but he knows all because he works in a gun shop.
I find there are 3 types of gun owners. the kind who think they wrote the book and wont hesitate to stick their nose in someone elses business to tell them what they are doing wrong. there is the kind who loves guns and loves to talk about them and share what he or she has learned, and there is the type who want to be left alone and don't even say hi. it seems most gun store employees are in the first category. besides where else you going to go?
unless your gun store is charging more than anyone else, just put up with the attitude and buy the gun. i don't remember what my .460 box said (I have since sold it) but the box is cut out for the 8 inch version - they don't have a custom insert for the 5 inch. just check the serial on the sticker and make sure you are not being charged for an xvr. if you go elsewhere you are likely to get similar attitude. check around online to see if you can find it for a better price and if so do mail order. the .460 if you have not shot it is SO worth it. the most fun handgun you will shoot. and the kick is not bad. it is worth putting up with some attitude to gain this beauty.
as for his attitude about glock - all the m&p is, is a glock clone! tell him that.