I get the whole “truth hurts” thing, but this is not a close friend, but a social acquaintance. There is a difference between being honest and being an asshole. Letting him know you aren’t interested in the watch, but thanks for your time is not a “political” way (although I have worked in Washington for 22 years so yes, I have mastered the art of telling people to go fυck themselves and still leave with a smile) of avoiding being the bearer of bad news, but a tactful one. If the OP feels the need to be “honest” with the fellow, he can simply say that he isn’t an expert, but showed the pictures to people who are and it raised some questions that he may want to investigate on his own- like at an AD.