The first little small town fair I did, I kept pretty good track of how many items each person bought. The majority of people bought one or two items. There was one person that bought four items, and two people that bought 5 or more items and one of them was actually a lady who have 6 teenagers with her. So at the next little booth I did, I put up a sign that said "Buy 5, Get 1 FREE." At that consignment sale, I had 3 people who bought that much to get the deal (and the sales overall were very slow/few). At the other little fair I did, I have 8 people buy 5 items to get that deal. They were all excited and a few told me they would be calling me to order more. One of them, booked a party. While I figure it costs me $3.10 to get people to buy that much, I'm figuring that it made me a lot more than it cost. I figure most of those people would have only bought 2 or 3 items each. Plus, they felt they were getting an amazing deal, will be future customers, and moved more product. I charge $5.50 per item (including the tax) so I came out ahead the money collected.
Another way to get more sales similar to this is to put up a sign that says "5 for $25." I know it is silly, but they are getting the number 5 in their head. Most people buy 2 to 4 items. This pushes the sales up to 5 items for some!
Before you do a "deal," think it through. When I have done a deal and people booked a party, they expect the deal at their party. And when someone else books a party from that party, they expect the deal too. If you offer a deal at your house when people come to buy, they expect it everywhere and tell everyone about the deal. I have told people that when I do a Special, it is at a fair, not at a party (but most don't like it!)