if i have an auction which doesn't reach the reserve price is there anything stoping me contacting the highest bidder and offering the item at the price they bid. or is this frowned upon by ebay?

Yes it would be frowned upon by Ebay as they would not get your commission on the sale.

But would they ever know?

He who dares !!!!!

the technical reason they give is that the buyer has no protection, but as Dave says, its the commission they really miss. I bought an item once that didnt reach reserve, and many times where i forgot to bid (and no one else did), never been caught out, and i cant see how they would find out anyway. Its safer as a seller than as a buyer cos he has to send money first.

should give you an option to offer to sell to the highest via ebay.

the item is a car and i specified that the buyer should pay cash when they picked up the car.

id do it. no harm in trying. and ebay cant leave you feedback anyway!

There is a thing called a second chance offer, you can use it if the highest bidder pulls out, or i think if your auction doesnt reach reserve. Go to bid history when the auction has finished and thet option should be there. Means you get feedback aswell