For the life of me I could never figure out how any wholesaler/dealer could offer any kind of warranty on AEGs. Just didn't make sense. Once it's out of your hands it's at the complete subject and whim of the user and these things are far from dummy-proof tanks. But to each their own I suppose.
However...on a one like you described....I would have done the cursory inspection and then said, "it needs a new mechbox and inner barrel....it's not worth piecing back together bit by bit". Faster on labour, easier on the forehead pounding (or blood letting in your case
)...cheaper on parts at the end of the day since the margins on AEGs are pretty thin when you factor in these kind of headaches.
IMHO...I would not have even bothered running a brush down the bore, aside from out of curiosities sake. If it couldn't be cleaned out with windex/silicone oil/hot soap & water and cloth patches over a plastic jag it's probably not worth the time/effort. Especially for a cheapo barrel. I have noticed that a lot of "clone" barrels will have horrible flashing/burrs at the hopup rubber cutout. Definitely sharp enough to score/scrape BBs as they pass by....easily deburred with a hard awl/punch.
As an aside...I bought a "BNIB" WE PDW the other night. One part (cosmetic) was loose and rattling around in the front end...other parts were loose as well. The inner barrel had factory grease caked all along it. As in 4 patches worth of grease before it was even approaching clean. All in all...no big deal to me since I broke it down to the smallest parts and carefully reassembled it anyways...but if a "normal guy" just took it out of the box and started firing mags through it it would have gone back to the retailer as defective out of the box.
I may be a bit out of touch with things...but I thought this years ago...aside from a TM, every AEG should be stripped down and gone over even if BNIB before a single battery and BB is put through it. And even then with a TM...all the screws and bits should be checked that they're not loose.