1. if you want to buy or sell at price X then why do you even care if someone places 1 satoshi above you! let them buy higher or sell cheaper than the price you have in mind!
Nope, he is right, this is THE most annoying thing that could happen while day trading, especially when you try to get a quick profit. That moment when you try to put a reasonable order to get picked by buyers/sellers, and find an annoying guy who keeps beating your bids.
2. pump a coin? you? i don't think you are big enough to pump an altcoin. unless you mean something else!
Yes, he can, anyone can, especially on YoBit – being a bigger fish in a small pond. You just keep buying the coin in small batches, then hype about it in the troll box, so that you lure traders into buying it (pumping it for you*). I think it's a low, cheap way to trade, though.
3. your statements cut in the middle of sentence! LOL.
I think he meant when you see a coin — you have been holding — pumping and try to sell, but it gets dumped hard.
4. simple solution: double check before clicking! and don't rush!
I think reputable exchanges (like Poloniex) have a prompt notification to confirm the order, which helps greatly.