#1 What is the value of the product?
To find out the value of the product you will have to use the product. There are 3 ways you could do that. You could buy the product and use it OR you could request for a review copy OR you could ask existing customers. After you decided that it is a good product, you will need to find out if it SELLS.

#2 Does the webpage convert?
This is a little trick to find out because you do not have access to the vendors sale statistics but there are some methods you could use. Firstly, visit the sales page and gauge for yourself how persuasive is it. Secondly, visit its listing in Clickbank via the marketplace and check out the stats there. Is it selling? How many affiliates promoting it?

#3 What bonuses does it give?
Bonuses are an important part of the buying and selling process, for some it could be the pivotal point in the buyers decision process. Ask yourself; are the bonuses some crap thrown together? Are they of certain value themselves? Would you be happy with the bonuses if you bought?

#4 How much can you make?
What is the commission like? Do not just blindly select the one which pays the highest commission! You have to take into account the price, whether people will actually buy from the site. You would be better off earning a 50% commission on a $30 book selling 2 units a day rather then earning a 75% commission on a $100 dollar software that sells 2 units per month.

#5 What kind of affiliate resources do they give?
Email solos, banners, classified ads templates and articles are just some of the things you could utilize. What kind of resources do they provide? Do they offer any help? Are these resources easy to use and impltement?

These methods are just a few ways you can determine if a product is worth your time and money promoting. Experimenting and testing is also a very important part of the whole affiliate marketing procedure. And most importantly, never give up!