Chainsaw Repair

We had a customer buy a CS-590 last week and he brought it back last night because he couldn't get it started. The other guy in the shop attempted to start it for a few minutes and was unsuccesfull. I tried to start it this morning and it would pop like it wanted to go but wouldn't. A little bit of smoke came out from under the clutch cover. The saw did not start and chain never moved. I noticed that there was fuel coming out of the muffler, so I took off the clutch cover in order to take off the chain break in order to take the top of the muffler off to look inside and thats when I realized the clutch cover was melted on the inside. The clutch spring are wacked out from all the heat, and a few other things are toast.

The customer said he never even got it started but tried pulling on it for hours. The only time it was ever run is when I sold it to him. I started it up and once it warmed up gave it enough throttle to scream for a second or two then I shut it off. No smoke and no smell of melted plastic. With the chain brake on could you even get the chain to spin on one of these things? Fortunately if it was my fault  The parts probably won't cost too much to fix it.
At this point I'm forced to believe that it was me since I'm the only one who ever got the saw running, but i just can't see all that damage happening with there being smoke or a smell of burning plastic.

Yeah that's what we're going to do. I watched the surveillance footage of the sale going down and from what it looks like I get the saw started and running with the chain brake on for maybe ten seconds tops (I maybe give it throttle for a couple secs, then I explain how to apply and disengage the brake) and it was so fresh out of the box I don't think it was even putting any power into the clutch yet. about 30 secs later the chain is spinning full speed with the brake off for about 4 seconds then the unit gets shut off and handed over to the guy. It was a crazy busy day so I couldn't remember everything that went down but I knew there was no way I did that without noticing something was going wrong.

I talked with tech service about it and they said you could also cause some damage if you push in the choke lever but never pull the throttle and then let it idle for 5-10 minutes with the brake on.

I picked up a cs306, rear handle Echo and it looks like the same thing happened to it. Chain brake partially melted, sadly also a scored piston.  Put in a new piston and a Caber ring.  Chain brake only 50% effective, but if I bought a new brake I wouldn't recover my costs.  Echo parts are pricey and not many used bits around.