That's where budget, space and all that other criteria I mentioned in the other thread comes into play.
Buying in volume will always get you a much better price than drop shipping, but drop shipping is low risk, where as buying in volume is high risk, especially if you don't know the market.
Of course if you are trying to reduce risk, then reduce the investment to do some test marketing. What you have to remember is that the data you collect may well be misleading if you try to build a business model around it.
Of course buying a couple of items to test the market with will cost you more per item than the real wholesale value, so if you put them on auction at your cost price to cover you bum and got no sales, it wouldn't be safe to assume it's a bad choice of product based on that result alone, because a wholesale price would reduce the unit cost and may put it into a price range where it would sell!
I hope that made sense lol. If you can, find the product you want to sell, check your market place to see what the competition is like, check their products, their sell through rates, etc.
From there if all is good you finally need to make sure you can compete on price, that will give you a more accurate picture of the market potential and cost you no money.