There needs to be a way to Invite potential buyers to your auction.

On the SP Marketplace you will find hundreds of other users who are commenting & bidding on auctions.

If you are a seller, you will particularly be interested in those users who are participating in an auction related to yours.

As a seller it is in your best interest to find qualified buyers. Currently you're free to contact users via PM so it may be an advantage to use PM's to contact users who may be interested in your auction. This is successful (I know because I received new bids over $10,000 by meeting people this way) however some people will regard any unsolicitated message as spam.

There needs to be a way to facilitate this process in a more effective way.

Invite to Bid
My idea is a "Invite to Bid" tool which streamlines the process of contacting qualified buyers who may not have seen your auction. Similar to Elance's "Invite Tool" which allows you to invite providers to your auction.

This way the potential buyer would receive an automated PM saying "(SP User) thinks you may be interested in his auction and has invited you to bid".

Since it's formalized, to the Seller can find qualified buyers and send them an offer to bid without the risk of being reported as a spammer.

There would need to be some restrictions of course. In fact, probably the easiest way to ensure Sellers are only sending Invites to those users who really might be interested, is to charge 1 credit per invite.