Hmm, exploiting the bug of selling artifacts for more than their face value has been prohibited since the Chaos League, where it was clearly stated in the rules. By the way, taking Hydra Nests is indeed a key element of quick gameplay (although I personally always do it manually, I don't like taking advantage of glitches), while selling them is a bug. Regarding how to trade correctly, artifacts should be sold in batches of no more than 5, starting from the rightmost slot. The next artifact to be sold is the one to the left of the rightmost, and so on, until you reach the leftmost position in the lineup. Since there are often more artifacts than that, to sell the rest, you need to re-enter the market and repeat the process. In this case, all artifacts will be sold at their actual value. If you always sell from the same slot, you will either make a huge profit or you might end up selling your entire inventory for a ridiculously low price :).