My own experience has been that, especially during a development cycle, companies where I've worked have been happy to save the 75-90% of materials cost that often are available on eBay. I've also found that much of what we buy through traditional supply channels comes from the same places that sell excess materials on eBay. After all, much of the stuff that's sold on eBay got to be "excess" only because it was manufactured and subsequently found to be surplus. Surplus does not mean junk. It means it's no longer needed. That may be because it was manufactured simply because it provided an economy of scale that wouldn't otherwise have been there. Often there are breakpoints in the pricing structure resulting from manufacturing efficiencies imposed by equipment and manpower rather than quantitative requirements.

One manufacturer for whom VCR heads (yes this was some time ago) were being made in a facility that built 'em in lproduction quantity. You started the process and, in order to make the first head, you had to complete 2700 of 'em, and that wasn't the most efficient way to do things. My employer, then, had to find a home for 2700 heads, when all he wanted was 450. The alternative, however, was to have none. They didn't have eBay back then, and I don't know what would have happened with 2250 such heads on eBay.

I've had pretty good luck buying what I had to have for prototypes, even in considerable quantity, via eBay. I've bought used test equipment, IC's, wire, cable, hand tools, etc, each with pretty good result.

If you spend any time looking at eBay's offerings, I believe you'll find that there's more risk than with Mouser or Digikey, but there's also considerable economy that's not offered by them.

RE