Note that on eBay and in most real-life auctions, a bid on an item from anyone related to the seller in almost any way, from friends and family to business associates and roommates, is considered to be a shill bid, will not be honored, and will almost certainly disqualify the sellereven if the bidder would have purchased the item.
What this means is that you can not buy from your family and friends on eBay, no matter what, no exceptions. That is the nature of auction selling.
eBay uses very sophisticated tools to catch shill bidders, so sophisticated that many first-time shills are surprised. Shill bidding renders you subject to suspension or other punishments, so be smart and don't bid on your own, or on your mother's or sister's or aunt's auctions, no matter how much you'd like to.