As the very name would suggest, these are for greeting a person to your store. But don't let that fool you into thinking that greeting cards are only meant for getting new customers to come in. You can effectively use greeting card printing with your current customers base.
The charm of greeting cards comes from the more formal nature of them when compared to many other forms of advertising. A greeting card isn't going to have the same push for sales that other advertising does. The best greeting cards will be more subdued and less direct in the way they advertise to a person.
Greeting cards are more about create an image for the company than getting a person to buy one product or another.
How much do they cost to use?
Greeting cards carry with them a rather small price tag. Please note that you will be getting a lot of them printed if you want to send them out to a large pool of people, so to save costs even more on printing, you would be well-advised to get as many of them printed at once as you can. Printing is always cheaper when done in bulk, so take advantage of that.
How exactly do I implement a greeting card push?
Just like with postcards you combine them with direct marketing for the best results possible. Find your mailing list of both new and existing customers and send them greeting cards inviting them to come in. You might create two separate cards for those who have never been to your store and those who are regular customers.
One way of getting more out of your cards as well is by attaching a coupon or other form of discounts to them. Now you've not only handed someone a nice invitation to come to your store, but you're rewarding them for doing so. You've just increased the odds of those people taking the time to come in and see what you're all about.
Are there any downsides to greeting cards?
I'd say the only major downside would be that this isn't something you can really do all the time. An approach like this works best if used only occasionally, or else it loses a bit of its charm. Certainly with those who have never come in if you keep sending them greeting card after greeting card, it looks like you can't get the message that they aren't interested, and you might turn them away even more.
