If it's their current bid you can end early (via the dropdown menu arrow next to the item on your selling list) and there's an option to sell to the highest bidder at their current bid price.
If you've agreed a higher price and there are no bids at the moment you can revise the price. Once they've placed their bid you can end as above.
If there are currently lower bids you'd have to end early, cancelling the bids in the process and relist at the agreed price.
