Ha! If you think those are insufferable annoyances, then I'm sorry to tell you that it gets worse. In fact, I posted a rant thread about some of those very kinds of things, just a few months ago.
How about the following?
* People who pepper you with all kinds of arcane technical questions, i.e. 'Does your XYZ model amp head use the original silver nitrate film resistors, or the later-model IC type?'
(Dude, I didn't manufacture the thing - and I certainly didn't design it. I'm just a player like you. I know a few basic things about it - enough to operate it effectively, and that's about it. If you need more information, find the manufacturer's manual somewhere online - if even they will answer your questions.)
* People who try to talk you down to an absolutely insulting lowball price by telling you all the reasons why your gear isn't as useful or valuable as you think it is - then feign offense and indignation when you refuse to accept their assessment. This is a variation of the old standby, trying to get something for nothing.
(Dude, if it's really as lame as you're telling me it is, then why would you be interested in the first place? If it's worth anything, it's worth a fair price.)
* People who make unreasonable, even outrageous demands.
(Several months ago, I had a pair of new boutique cabs for sale, something that's been getting a lot of attention around here lately. Some cat over in Brooklyn sent an email, expressing great interest and asking if he could come over to my place with his bass, to play through them and check 'em out - no word about actually purchasing them. I actually had to explain to this guy that, a) I'm not a dealer, b) I don't have a showroom, and c) This isn't Sam Ash.)
(More recently, I had an SKB rack for sale on my local Craig's List. Got a message from some guy who explained that he didn't mean to lowball me - then proceeded to go right away and do so anyway. I managed to negotiate him up to a price that was somewhat less insulting. He replied by offering to stop by my place, or suggested that we meet in midtown - even though I don't make it to midtown Manhattan very often these days. I politely replied by giving him my address, driving directions, and offering to be available at his convenience. He then replied by asking, "Uh, but not midtown? See I work in midtown, and I was figuring you could just swing by my office during business hours..."
I replied by stating: "Let me get this straight. First you lowball me on the price. Now you want me to go out of my way for the privilege of 'winning' your business, by delivering it right to your door as well. Will there be anything else? A complimentary shoeshine, perhaps?")
GLWTS...
MM