Seems like a bit of fear mongering going on here. I've got a 590 and a 600 off ebay for just over $200 (each). Neither were running, but about $10 later in parts they were, so it depends on your tolerance and skill level in doing repairs.
If you want a no-hassle running out of the box with warranty, don't look on ebay. What you posted looks
really nice, so if you don't care about warranty, ask them what the deal is. e.g. is it a return as others have suggested, does it run, pull over, etc.
It states open box and a 30 day return so... if I were looking for new-ish, I'd jump on that for that price, but I'm also content rebuilding the whole thing if I need to at some point. For the price in the posting I'd expect it to run and not have a melted piston.
All that said, they're great saws for what they are (part way between homeowner and pro?). Surprising power, muffler mod helps. The 600 I got (effectively the same as the 590) went full 24" bar with the depth gauges pretty much filed off (how I got it) and pulled it with minimal complaint. That's pretty impressive for a 60cc saw. Either that or my filing skills are better than I thought