Does your product require a payment, before the user is able to place a bid? That is possible, you can enable this option in YITH > Auctions > General.
You can set this rule in the ‘general‘ plugin settings, and decide per product if you want to disable it and/or change the default fee amount.
You first decide IF you want to override the general settings, and you then decide how you wish to override them.
The user will see a warning message on the product page, explaining the need of a fee.