What is eBay Best Offer
Best offer is an eBay feature that allows you as a buyer to negotiate the price of the item. It allows you to get the item you want at the price you're willing to pay, assuming that the seller accepts your price.
Why use eBay Best Offer
If a seller listed an item as Buy It Now and added best offer option, this means that they are willing to accept less for the item than Buy It Now price. If you find an item that's priced close to what you want to pay and it has best offer, you might be able to get a good price. Just make sure you've researched completed eBay listings so you know what this item is selling for on eBay.
Also, when you submit your offer, seller can come back and give you counter-offer which should be lower than Buy It Now price.
Best Offers can save you money
I've had some success with best offers. Several months ago, I was able to get an item for $1320 where seller was asking $1450. I was very happy with this deal. After doing my research on completed listings, I found that similar items were selling for $1400 - $1450. I also noticed that this seller just made a lot of money selling something else by searching for completed listings by seller. I figured that he'll be happy with the other sale and he might sell me this item even if he has to take a loss just to get rid of it. I was right and he accepted my offer.
I also had a lot of best offers declined. I learned that if you offer unreasonably low price, seller is just going to decline. If you submit reasonable price, even if seller does not accept, they might send you counter-offer. If that happens, you can decide to accept it, submit another counter-offer or just move on to the next item.
Unreasonably high Buy It Now prices
Some eBay sellers set Buy It Now price that's way above market value and add second chance offer. I usually don't waste my time with those listings as those sellers try to be slick and will not give you good deal.
I don't specifically look for best offers but when I search for something on eBay and I see a decent Buy It Now price with best offer option, I'll look at it to see if it's worth pursuing.
Best offer is just another tool you can use to find good deals.
If you're interested in other way to save money, take a look at eBay software that I've created called Buyer Auction Manager. It's for eBay buyers and it will help you find good deals and save you money.