I've exhibited a bunch in non-traditional spaces (restaurants, bookstores, cafes). I have had no problems with exhibiting there, and I have actually made some sales. Most of the time the deal has been very basic - your work goes up, they reap the benefits of your beautification of their space, and they direct anyone who wants to buy something to you, so there is no tax and no commission involved. If something were to happen (artwork falls on a patron, for example) that would be covered by the restaurant's liability insurance, although you'd probably be out the price of your piece of artwork. If you have a good working relationship with the restaurant/store owner, I would think they would try to work with you if your work was stolen, as far as filing an insurance claim with their insurance, but in all likelihood, unless your artwork is selling for multi-thousands per piece, at which point you're not selling in cafes anymore, you are probably going to fall below their deductible. It is just a risk you have to take. So far, (fingers crossed) I've been lucky - the only work I ever had lost/damaged was in a group show at a large gallery (a photo fell off the wall, the last day of the show, and the glass broke and the frame bent).
All in all, I'd say it is a positive, beneficial arrangement to show in restaurants/cafes. If you can afford the framing for the show, I say go for it.