[bingo cards] is not a huge fraction of my business (4%ish) -- [bingo card creator] (with both brand & generic intent), [bingo card maker], [make your own bingo], [custom bingo cards], yadda yadda yadda, and then I start getting longtail searches from about a thousand activities which cover most of what an elementary school teacher could want in a lesson plan. Obviously, most of them don't contribute a sale in any particular month -- heck, 80% of them have yet to contribute a sale ever -- but the aggregate economics work out to staggeringly efficient. This is one of my Big Ideas, see the greatest hits section on my blog for it done to death several times over.

Every reason people have for buying bingo cards in September is a reason to buy bingo cards in October, plus the various promotional activities, plus my AdWord spend goes vertical after around October 15th.

Normally, my AdWords performance is constrained by inventory: I could literally buy every click available for sale from Google for the keywords I care about at prices which make sense to me. When I don't bork the heck out of my conversion codes, I'm also inventory-constrained during Halloween, but inventory levels are much higher than usual.

Didn't you depleted prospects pool reachable by use of your current marketing channels?

It may be the time to think about other means to reach new sets of prospects.

If you have any suggestions, I'm always willing to hear them. But no, there is no way to square the hypothesis that I've depleted prospects available with my current marketing channels when the sales chart keeps going up and to the right.

Organic SEO (and by extension AdWords) is like a river: water goes by today, either you get it or somebody else does, but there will be water tomorrow. The total market is far, far larger than my capability to service it. (There are 3 million elementary schoolteachers in the United States. I have 3,500 customers.)

The nice part about email is that it lets you "store water" if you follow the analogy, since loss to evaporation is just obscene in my business. 80% of people who signed up last October never logged in again after 48 hours from their signup. Many never logged in a second time.

I'm fully aware that you didn't reach substantial part of your total market yet.

One suggestion: a means for your customer to tell or email a friend to get a discount for both of them (by Dropbox example).

What does it mean to give someone a discount after they've already paid? Are you paying them money?

Some companies do, especially if the referrer has an account for the service. This might be hard for one-off sales, but discount codes for additional or add on software could be an option.

Facebook? I actually see some real, relevant, and useful ads there. And there are a ton of teachers there, avoiding working on their lesson plans.

Tried it. Paid $200 to get three sales of $30 software. Nearly tipped a virtual cow in frustration.

Just curious but was that on a CPC or CPM basis? I've always theorized CPM based advertising on Facebook is useless since the page gets reloaded so often.

Direct (paper) mail?

I might consider that for AR, but at $30 LTV the economics of mail are just punishing.