I have 2 suppliers producing similar (but with distinct designs) items. One of those almost killed my business! I buy and sell the item after I get the order... so I had this product from the 2nd supplier and had put up the images of it, which was purchased by a customer. I had to buy the item from the 2nd supplier who is a new supplier for me btw, and dispatch the item to the buyer --simple task which was done successfully with the 1st supplier many times in the immediate past).
NO! The manufacturer/supplier told me on phone that the item is in stock and I can take it away... I went to him and he told that the item just was sold to another retailer... he said I can get it the day after... again I inquired the next day, he said it is ready, but when I went there the item was not the exact design and color as shown on my ebay sales page... it happened the next day too after getting a promise that he will manufacture the exact same item as displayed, immediately. I had to cancel the order and it almost got me a negative feedback in the process -- it would have been my first! So beware, and get a trusted supplier first.
Such serious mixups are bound to happen if you don't stock the item, or if you don't have a trusted supplier, or you're plainly unlucky. Think of a few plans of what to do to get out of a nasty situation in such eventualities! I was caught up unexpectedly...