If you mean you made a Best Offer and someone else's offer was selected, you don't. eBay does not tell the actual amount of an offer in public places (you used to be able to get an idea of what it was by sorting a sold items search result by price and it would be put in the proper place for the actual price in the sort so you know it was equal to or more than the next highest price below it and equal to or less than the higher price immediately above it, but I think eBay got wise to that trick).
If it ended with an auction (someone bid on the auction after you made your offer) then the final price is accurate. Or if someone else used the Buy It Now after you made an offer (or bid and the BIN remained up in certain situations) that price would be accurate. If it is an auction format listing you can click on the number of bids display on the Listing Page (either the short form one that comes up when you click on a link to the item or the "Original listing" linked on that short form) to get to the Bid History Page and if there is a Buy It Now or Best Offer logo at the winning "bid" amount then you know that's how it ended. If the status at top left of the Listing Page says the seller ended it early then either s/he relisted it--there may be a link there to the relisting--and either sold it to someone making an offer in a message or s/he sold it off-eBay, or some issue came up where s/he didn't sell it.
