very weird.. i never had any issues with them .. you should've just sent it back, as you DO have a 30 day no questions asked money return guarantee.
i did have an issue with musikhaus.de .. though it wasnt THEIR fault, that the amp sucked.. so, they're ok :P i called them after two weeks, said i want to return the amp since it wasnt what i hoped for, they sent an UPS guy over, took the box and i got all of my money back. thomann as far as i know has exactly the same policy.
if you told them, the product arrived damaged, they would've taken it back.
it is possible, that someone did the exact same mistake that you did, sent it back on terms, that he wasn't satisfied with it.. and i doubt they test EVERY product they get back (had a friend who had a job testing returned stuff and.. they just see if it turns on and that's about it.. unless it's a lot of fun to play with.. like an RC helicopter), before they return it to the shelf for further dispatch. you probably just got unlucky, cos i really used to order from them a lot.