I don't understand sellers who act like assh0les to every potential buyer, that is not how you sell anything... Be as courteous and helpful as possible to everyone (until you realize they are not a serious buyer), they will trust you more and be more inclined to buy from you instead of someone else.
I haven't sold many vehicles, but I did sell a LOT of computer equipment over the years. You are starting with the premise that everybody making inquiries is also a serious buyer, but in my experience that is never the case. For every serious buyer there are at least 4-5 tire kickers, and at some point you learn to figure it out within a couple of emails, or a couple of minutes of conversation.
Now I make it a rule to price my stuff at 10% more than market value, just so I have a bit of negotiating room. Everybody wants to haggle, so if you start with your bottom dollar then you invariably get less than what the item is worth.
I've had literally hundreds of people write messages like these:
Buyer: "I can offer you 10-20% less than your asking price."
Me: "Ok, come pick it up."
Buyer: "Sorry, my car broke down/dog ate my debit card/other blatantly false excuse. I can't afford buying your item anymore."
Buyer: "I can offer you half your asking price, will pay CASH!!!"
Me: "So I take it if you were to meet my asking price I'd have to accept a post dated cheque from the Central Bank of Zimbabwe?"
Buyer: "I will offer you your asking price. But you have to take out the hard drive or RAM because I already have them, and subtract brand new price of hard drive or RAM from the price."
Me: "And what exactly am I supposed to do with the extra stuff?"
And many other examples... That's partly the reason I got out of the buying and selling racket, most times it's not worth the hassle. I traded in my old SV when I picked up my GSXR, and while I lost about $5-700 on the deal (after factoring in the HST deduction), I figure my time and sanity were worth it.