If you wish to control whether a user can bid on an auction (through buy it now or standard bids) within your site you can use the account verification feature in conjunction with the "must be verified account to bid" admin setting. This will force any user within the software to be verified before they can bid on an auction within your site. You must first enable the account verification feature here in the admin tool:

SITE SETUP > USER ACCOUNT SETTINGS > Enable account verification system

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Then you can control the ability for this feature on a price plan by price plan basis. You would do so through the following admin tool setting within the price plan cost specifics admin tool page. Within the

PRICE PLANS > [EDIT] (next to price plan) > COST SPECIFICS > SCROLL TO PLAN ITEMS SECTION > ACCOUNT VERIFY ITEM

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This will force account verification of that user's account before bids can be made on an auction. How you verify the account is up to you.