affiliate sales generated $35.80 profit per unit by his numbers ($55 - $15 affiliate - $4.20 unit cost). I get the impression that affiliate sales were face-to-face and not the bulk of his business, although I might be wrong here.

I was purchasing these products for $4.20 each [including shipping and handling] so I could afford to undercut the competitors by a significant margin. A buy it now (BIN) price was put as $49.95 -- this would give me a $45.75 profit, minus the eBay fees which brought the profit down to around $40.75.