robgul
Barry Bucknell is my hero
If the deal is good moneywise without the fence, then go ahead and allow him to send the item with (or not the refund he offers). If the item/price without the fence is not a great deal allow him to cancel the sale. All he has to say is item broken or missing and the sale is finished, ebay will automatically send a refund to you.
As others have said if you wish nothing to stop you bidding again and I suggest (I have done this successfully in the past) you bid a price that you would want to pay straight off (so you don't have to keep bidding a little more every day or so) -- then as other bids roll along yours will still remain top unless your bid is outbid. If no other bidder come close to yours then you only pay a nudge over the next closest bid (not the max you have bid)
If he sets a buy it now thats something else to consider.
Taking your second paragraph about bidding - I only bid on ebay using Auction Sniper - I set the max bid and the system fires of my bid 3 seconds before the auction ends - that way you're not exposing your max to other bidders that may creep up until they pass yours . . . . the service costs peanuts and is worth it - I've won lots of items with lower than my max bids.