FranP I think you were unfortunate. We have never had anything like that happen to us - and we have been buying and selling at auctions for over 50 years.
However, the auction price for something will always be considerably less than the retail figure. An antiue dealer selling a table for £150, will expect to buy it for £75.
The other thing is that at an auction, even today, with telephone and internet bidding there can be no, or not many interested bidders, so the item sells cheaply. This is why one puts a reserve price on an item. to make sure it does not go for little or nothing.
It is always instructional to watch something like 'Flog it'. You will see examples of all the circumstances I have mentioned above in every auction. We have sometimes been shocked by how little we got for some lots we thought should so well and how much we got for other lots where we had few expectations.
At the end of the day an auction can be a risky place to sell.