If you mean do you have to sell for the final price of the auction even if there is only 1 bidder and is therefore the Starting Price that you set), yes, you do. It is very much against the User Agreement you signed (and for which you get a "defect" that counts in your monthly selling status evaluation for the next year if you cancel or make the buyer "Ask eBay to step in" to get his/her money back), and a breach of contract for which you could theoretically be sued (it's generally not practical but it is within the law) by the buyer if you don't.
Set your Starting Price at your TRUE minimum that you are willing and able to sell that item for (don't forget to figure in the fees on the price plus s/h plus sales tax for the majority of buyer's states). You can set a Reserve Price (but that comes with high fees that are charged regardless of the outcome of the auction AND discourages bidders from bidding) for the privilege of setting a lower Starting Price without having to sell below the Reserve amount, and schemes to avoid selling for as low as the Starting Price are a violation of the rule against avoiding the fee.
If you mean something else you need to explain what you meant. It is eBay who will "accept" a bid (as opposed to a Best Offer) if it is a valid bid at the time it is received (e.g. meets the minimum bid amount, the bidder is not blocked by your Blocked Bidder/Buyer List or your Buyer Requirements, the bidder is within his/her buying limits).
