What is a Reserve Price
Reserve price is the lowest price at which an auctioneer will sell the product via the auction process. The auctioneer is not obligated to accept a winning bid that is lower than this price.
Given below in the image there is a field to add Lowest Price.
Create an Auction product. If you don't know how to create an auction product then refer to the How To Add Auction Products Manually article. After creating an Auction product add the details of your product and save/update the product. Visit your product detail page and you will find the Reserve price has not been met text.
When someone's bid is more than Lowest Price then the text will change to Reserve price has been met text.
In the Ultimate Auction Pro plugin If all active bids are lower than the reserve price and the auction expires then there will not be any winner for that auction.