My purchases were profitable. They would be mostly thin-tired ten speed bikes in broken condition. So I doubled my money just on the wheels. Of course it wasn't all smooth sailing. Some of the wheels needed alignment, and the bikes needed repair.
Parts do sell better when they are cleaned up.
But, if you gather a large collection of such things, you'll have a large clientele coming for them. Treat your clientele well. I think the most important factor in growing your business is to have a high ratio of customers who go away satisfied. For instance, if you have more people coming for steel handlebar stems and upright handlebars than you can supply, get some new ones from a wholesaler. The people who came to your junkyard are hoping for very low prices, but if all you have is something new, at an average price, they'll typically buy it, and be satisfied.