I think there's a few factors here that I'd like to comment on.
First a communication issue, which on a place like this many people only login once a day, and check the messages reply and then leave, so if they're trying to buy a lens and I say I would like this lens but I'd like more information on it what is the price or would you ship to this place, and in the meantime other people are contacting the same seller and/or buyer and saying oh I'll take it right now should the seller wait to answer the questions of that person, or should he sell it to the person who is actively ready to buy at that moment. It's really a factor of being polite versus being business savvy. And Innoway it's a version of what is polite for now versus what was considered polite in the past, I think that the older generation believe in taking your time and expect people to be honorable, but the new generation sort of are more trained to simply sell to the first purchaser and not wait and be polite to those who have already been in discussion about something. However, after having bought and sold a bunch on here, I've learned that people often disappear even sometimes when they seem honorable, and so you kind of have to just sell to the first person that comes along otherwise you end up with A lot of waiting, and often disappointment when that person disappears and the other buyers who came after and had the money were not willing to wait and bought the item somewhere else.
On the second note about price, often times I see things on here that are valued way higher than I would expect to pay, and also things that are of average price, and things that are low priced.
If I see something that's really high and it sits for a long time, sometimes I will contact the buyer and suggest that they lower their price and give them information as to why any private message, I think that this is at least a little fair, some people might be angry at this, but it also is sort of unfair to ask someone to pay for something that is way higher than it should be.
There's also the aspect of what the "common asking price" is of something versus it's actual value, often times lenses for example are available at a given price and everyone knows that Exline's sells for $600 and that's the asking price for almost everyone, but there happened to be a surplus of those lenses out there and so why would I pay the same exact price when there are so many lenses available why shouldn't I suggest to the seller hey I'll pay $500 instead because I know that it's a supply and demand situation and why should I pay more when I can pay less, if the $600 range were truly the asking price there wouldn't be so many out there because people would have bought them already, so it shows that for the value they are overpriced in this given market buyers and sellers etc. That's how I see it anyway.
So yeah I will send someone a lowball offer if there's tons of the same item available at the same price obviously that's not a very good price or they all would be sold...
I also personally hate paying shipping, and I think it's sort of funny when people who sell in the US only refuse to eat the $12 shipping cost on a $600 item, it's like a little stab wound for me, so I always offer $600 even with something like that. And no I'm not paying your PayPal fees either, if you choose to use PayPal then you should except the fees involved in the protection that PayPal gives you and not try to weasel it out of your buyer, I also find that insulting. I know it's all perspective, you could easily build that into the price of the initial item, but I think it's just really annoying when they try to build it into the additional costs afterwards.
Not sure I covered everything but these are some of my thoughts.
When the item doesn't sell they will find out that they are asking too much. 
