A marketing dream is to get your message to your target audience at the lowest cost and highest return. Targeted mailing lists, or leaflet drops through the neighbourhood doors often are typically read by only 3% of those that receive them - and the conversion rate of those 3% into customers is even lower. A leaflet drop of 10,000 might be read by 300 potential customers, but a good return would be for 10% of those 300 to become customers - 30 people out of 10,000 - 0.003% return on investment.
Then you must look at the cost of producing the direct mail or leaflet drop, and compare against the profit you've made on the sale to those 30 people. Was it worth it? Would you have been more profitable had you not done anything?
That's why we believe customers receipts are a tremendous opportunity. You'll already know how many receipts you issue, but if you're going to print a message to encourage the customer to do something that will make you money, you need to get them to read it first. 3 lines of text in the same font as the till receipt is not going to be noticed by the customer, or it will be forgotten about quickly.