Earlier in the year I bought some stuff from UK clothes retailer USC. USC kindly included some gift vouchers in my delivery.
This is a good example of how to sweeten a deal and make your customers happy.
The vouchers did not include any expiry date on them. I banked them until the autumn, so I could maximize their potential by using them in conjunction with a heavy winter coat. I recently spotted a coat I liked a lot. It's a bit pricey at nearly £200, so I decided to cash in my vouchers.
Unfortunately, the vouchers didn't work Frustrating! I emailed the company to ask them why, and it turns out that -- despite not including a printed expiry notice -- the vouchers had expired. I asked the company if they would be willing to issue me with a replacement voucher, and they stopped replying to my emails.
This is a good example of how to really sour a customer's impression of you and make them look elsewhere. I did so, and found another retailer selling the coat £20 cheaper.