Chainsaw Repair

I have a 4 year old Stihl 290 that my shop hasn't just told me is junk because of a scored piston and cylinder. I brought it in because it sat for a year and then would not start. To say I am shocked is not exaggerating.

First, how does that even happen to a machine that is not opened up?
Second, is it really that expensive to fix? A new one is $500. I can't believe it is that much to fix - but the shop suggested I just buy new. Maybe I should seek a second opinion?

I have to agree with the previous comment. The domestic/farmer Stihl chainsaws use a clamshell type engine which is very labour intensive to remove and re-build- then of course you have the cost of a new genuine piston and barrel (if it's a Stihl main agent) as a dealer won't just fit a piston even if the barrel is just slightly scored. He won't want you to bring it back and blame him for doing half a job, so to guarantee a repair they will err on the side of caution- hence the cost. Stihl pro saws use a different engine style and although the saws are dearer to buy, irinically they are quicker, cheaper and easier to repair.