How much to invest

The first rule when it comes to advertisements is that you must not invest more than you can earn. For example, if my commission is $10 per sale, my monthly fixed costs are $25 and I invest $50 and got 100 visitors, with a 5% CR I will lose $25.

In order to make a profit I need to have at least 160 visitors when spending $50 on advertisements.

So, before you decide to use advertising media, check if you will get enough visitors in order to earn enough.
Furthermore, the amount of your earnings depends on the % CR and your actual commission. You can run a test by investing enough money so you can get around 100 visitors to your website each day for about three months and then calculate the % CR and the actual commission. Depending on these results, you can plan the next step. The following scenarios are possible.

First scenario: % CR is between 2% and 5%. Actual commission is less than estimated.
Example: I have two products: one has a $4 commission and the other a $6 commission. From the 100% customers that bought a product, 80% bought the product with a commission of $4 and 20% the product with a $6 commission. My estimated commission was $5, my actual commission is $4.40.
What you can do is find out why customers don’t buy the high commission products. Maybe the quality is not good enough, or maybe they are too expensive. I must admit that this scenario is mostly unlikely to occur.

Second scenario: % CR is lower than 2%. Actual commission is less than estimated.
The moment that you have less than 2% CR you are doing something wrong. Maybe it is the products or services, the content of your website, or maybe you missed something while you were analyzing the market. Try to find out why customers aren’t interested in your product or service. And once you have fixed the problem, try again for a couple of months and see what happens. Keep trying until the fourth scenario occurs.

Third scenario: % CR is higher than 5%. Actual commission is less than estimated.
This scenario is ok if you can reach your financial goal. Still, I would recommend finding out why customers don’t buy the high commission products.

Fourth scenario: % CR is between 2% and 5% or higher. Actual commission is as estimated or more.
Congratulations! You now have a financially healthy business.

Note:
Don't be discouraged if your business is not making profit. Some businesses start making profit in a few months and some take a year and others years. It all depends on product or service that you deliver. But if your marketing analysis was done properly you should make profit. Don't give up, find out why your business isn't making money and fix the problem.