So in other words the restaurant barters meals and gets "trade credits". The other participants barter either the products they are selling "plumbing supplies" or services "lawyer, accountant" and so on. They get trade credits. The barter exchange keeps track of how many credits a business has so they know what they can spend. Typically people who sell services or perishable products are big winners. Losers would be businesses with low margins. For example you wouldn't find any Plasma TV's typically on a barter exchange. You might find jewelry though because that has a big markup. I actually was able (and this was some time ago I have to add) barter an apartment for myself as well as apartments for some of my employees. Other big items are perishable products such as hotel rooms, travel and so on. Magazine or newspaper ad space are other examples.
Use it or lose it to the vendor. There is an active and most likely a separate channel of travel barter that operates independent of any barter exchange. (Billboards for radio time let's say. TV for travel expenses.).
So I guess in theory someone taking groupon (or barter dollars) should just be a regular business that is doing well wanting to increase business. But in actual cases it might more often (from my experience at least) be a marginal business that is trying to fix a situation with marketing that isn't exactly going to work as planned by bringing in groupon dollars or barter dollars (that will end up being used by the owner to go out to dinner with his wife (and yes that is what happened)). Valuable things (in the case of barter dollars) that a business needs are not typically available with barter dollars. What you get is a bunch of things like dining, travel or accountants or attorneys (and how many of those do you need).