This is a common problem when your dropshipping. You have little to no control with the products you sell. Prices can change, the product may run out after you made the sale. And many other problems like paypal frezing your account or ebay locking your account because your a dropshipper and they dont like dropship sellers.
Your best bet is to avoid dropshipping and buy pallets of products to sell. You can buy pallets from as little as $100 and up to $1,000 based on the products you want to sell. And 90% of the time you buy pallets your getting items at below wholesale so the majority of items you sell gain you a profit.