Did you take it back? Or sell as is?
You must have had iron brackets or hardware on it. If it sticks to a magnet, it needs to be removed.
Wanna hear something funny?
I was about 15 or 16. Took some aluminum in from an old camp trailer. Totally new to scrapping.
Guy says "that's dirty. we'll pay more if it's clean". (it had dirt on it, I thought it was silly but okay...I wanted more $$.
Took it back home, washed it off and came back.
Yeah...that wasn't the kind of clean they meant. lol