there is great money to be made from 2nd hand store 90% wouldnt really know the scrap value.
you could offer free pick up of there unwanted items.I have 2 whiteware shops I grab what ever i want out the back plus a deal with 4 computer stores for their unwanted junk (he he he they dont know theres gold in there hills).they are happy not to pay to have it dumped and your happy with the unwanted items.
I say go for it dont hold back to what stores you try.dont need to be 2nd hand stores either main stream have trade ins and dumpers to
good luck and happy scrappin