The Exchange rules are clear, but it does no good unless people read them.
When you are the seller, you can dictate your own sales terms. You need to provide reasonable contingencies in those terms to handle potential tire kickers that may not be all that serious, or new folks that do not understand the way the Exchange works. Unless your terms are stated clearly in your sales thread, no one can guess what exactly your expectations for payment or communication are. Again this is all on the seller to make things clear, blaming the potential buyer isn't going to work.
If someone repeatedly flakes on deals by committing to buy then leaves the seller high and dry, that can earn an infraction or a banning. There was a member a while back that would buy a knife on the Exchange, then turn around and start a complaint/hate thread about the item not being as described, noticing microscopic "flaws or damage" that came from the factory, shipping was not fast enough, the seller was dishonest about the most mundane things, etc. It happened about 4 times until we banned him. There was no other choice. There must be a clearly visible established pattern of this before anything gets done. We aren't going to turn into tyrants and start banning people for changing their minds on one deal. Mistakes happen and people can jump the gun when new. Being a bit patient is more valuable than being inflexible.
So if you state the following or similar:
1-Item will be listed as available until payment is received, or unless we work out some other arrangement via email.
2-Prompt communication and payment is expected within 24 hours or the item will be sold to the next person in line
3-Serious inquiries only please
4-No low ballers please, low ball offers will be politely ignored
Number one takes care of the communication problem, there is a clearly stated timeframe in which to do business. It also provides documentation. You need to CYA at all times, document everything via email keep emails, and don't state something which you don't mean and will later be used against you.
Number two sets the expectation regarding payment. No one can say anything about not knowing what you the seller wanted. Again this has to be reasonable. Not everyone lives on the forums, or has access to them while at work. Some people have families, or health issues, or more than one job, etc. Not everyone's life is the same cookie cutter pattern as yours.
Number three takes care of the flakers and sets a warning that serious inquires only will be considered. No need to lead people on and it is hard to extrapolate something other than what is written.
Number four takes care of the tire kickers "I'll trade you 15 Sanrenmu 710knives, 3 marbles, and a LNIB pair of socks for your Sebenza" type of people.
In the end it should be a nonissue, depending on how you write your terms. Keep it simple, brief, and polite. Don't give people the impression that you are a diva on the Exchange and hard to deal with. If you still have problems, report the posts or the issue. If it is something we need to intervene in, we can and will try to open communication with people. Failing that, move onto someone else. Life is short, don't get hung up on the little stuff.