You may get in game mail from idiots and may even get some player reports, but as long as your activities are within safe bounds you're fine. For Example: I had one competitor in the glyph market selling glyphs at 20g when the "going price" was closer to 90g this was the state of play for several months. At first it was annoying seeing all the protential profit go to waste talking to him was pointless and blizz would do nothing as there still was room between cost and his asking price. The trick is to see the potential for increased profit. In this case I simply bought out 2/3 of his stock stock piling them, allowing the otyher 1/3 to be bought by the popolus - it took a few weeks but eventually he couldn't keep up with the demand and especially with the changes to the ink vendor folded. He probably made 30K or so. NOW I am sitting on 2 gbanks full of glyphs that are selling at 45g MINIMUM 200g MAXIMUM. Yesterday I made 13K from glyphs alone (and i coulda made more if i cancelled undercuts and reposted but cba tbh). I've kinda wandered off topic but the point was meant to be that you might get some "aggravation" but take it as a good sign it means your making a dent in someones back yard, and more than likely there's potential for more exploitation for more gold making.