It really comes down to the individual supplier as to what sort of deal they are prepared to do for you. Some may be willing to nego a price on a lower MOQ purchase, but I doubt any will actually sell you a one off product at anything less than their list price, despite the offer of coming back to purchase more if the product is as they promise.
The problem is of course that they don't know if you're genuine or not, you could well just be someone looking to buy the product for yourself at a bargain cut rate price. Perhaps if you had a solid trading record you could show them, then they would perhaps see the benefit in providing a free or at least cut price test product.
I'm afraid that you're quite limited in your options on this one.
For what it's worth, I think it's actually smart buying a test item yourself first before taking a wholesale order and openly marketing it.