This is the whole problem with Member Auction Links - you don't have to be a member for say, 90 days or X points before posting.
So what else do you do? Classifieds is cumbersome because each sale thread has to be approved, even for a half-decade member with thousands of posts. That's why you often have to drill through pages of ancient history to find what is actually for sale today, back on page 1, which was recently modified but originally posted years ago.
Linking to an external auction at least means that somebody else is enforcing the honesty of the seller. A new member on this forum listing an item for sale by a zero-feedback ebay seller - now that would be decidedly fishy.