You can increase sales quickly by giving your customer a gift they would consider adds value to their purchase. But don't go cheap, you really must provide value to get the sale.
A follow up note contains a packet of flow seeds and a note, "We'll make your business bloom" with a simple phone number as a call to action is NOT how to use a gimmick. Grabbers are an excellent way to get your prospects attention if you know how to use the the right way.