Ask yourself if you will have the inventory to meet expenses each month, and be able to make a profit as well. It is very hard to find dependable suppliers of quality products for resale. Some sellers do have established suppliers, but the majority of non-business individuals most likely buy at flea markets, private sales, garage sales or sell off their own unwanted goods. Some use drop shippers (most of us don't recommend this and read why
here), and of course many sell their own handmade products.
You can ask, many do, but sellers will likely not divulge who their wholesalers are, if in fact they are dealing with a wholesaler. Many will be dealing with jobbers, not wholesalers. Jobber is a level between wholesale and retail. Don't take it personal, these sellers have invested too much time locating their suppliers and they aren't about to give that information out to someone else.
Also, unless you are an established business with a business/tax license who is prepared to purchase large quantities, most reputable wholesalers will not deal with you. They keyword here is reputable; there are lots of people who represent themselves as wholesalers who are not. The only thing I can suggest is research, research, research.
Whatever you decide to sell, again, research, research, research. Search through eBay listings. Is there a demand for your product, what kind of competition is there in the market you will be selling in, and is that market already flooded with these items?
Then research if that product is selling (through a completed listing search). How many are being sold, how often are they sold, what prices are they getting?. You may find there is too much competition to cover your costs or to make any decent money.