Suppose someone started an auction at 10d. I bid 10d. Noone else bid. Can the seller simply stop the auction and tell me that he cannot give it to me at the price that he set because he finds the price too low?

No, not really... but people do it all the time and it is not really punishable. I would tell you just not to auction from him. It is kind of sly when people do that thing and it isn't very nice, and its looked down upon, but people do it none the less.

Require that seller disclose if there is a Reserve Price for each auction. Take a screenshot. If there is, they can do it and get away with declining the sale.

If there isn't and the sale is declined, forward me the relevant screenshots and a ban from using Tradechat will take place. Same goes for non-paying buyers. Tradechat is already spammy enough, players who contribute to this by forcing an auction restart will be barred from using the system.

As long as everything is disclosed ahead of time this shouldn't be a frequent problem.

Edit: Horrible color choice.

I am a kind person, usually never do report...

but just out of curious, if someone place a high bid on certain item, does it bind?

What if he "pull out" before the 3rd call??

again, I am a kind person, usually never do report...

I get the impression that users making fake bids on serious auctions will be dealt with. Anything questionable ("OMG I BID 99999 diamonds!") should be probably be verified ("Ov3r_b1d, are you really bidding 99999d?") and if they say they are, then I'd file a report. I'm a nice guy, but I don't think that blocking people from misusing public resources is "being mean"-- if anything, it's being nice to those that actually want to use them properly!