How do I know if my Affiliate earnings are being stolen?

1) Check your Statistics at the affiliate program.
Where are your statistics coming from with 600 click throughs? If they are your own web statistics, do they match up with what you see from Buy.com's affiliate reporting? All that counts is the affiliate program reporting, not your web host reporting. If the program matches your reports, then it could be poor targeting. Some web reporting count bots who crawl your site as clicks.

2) Are you having a technical issue? Really this is the same as #1 above. If Buy.com is reporting the clicks for your affiliate account, then they're valid.

3) Is your targeting off? Are you getting people interested in buying to Buy.com or info traffic? If you are getting targeted traffic for the keyword "Sharp Aquos LG542313 install", those are probably people looking for manuals and not buyers of the TV itself. Do your keywords target torrents or something children who have no buying power are searching for?

4) Are you tricking people into clicking through to Buy.com? If you aren't sending people with a buying intent, they'll never buy. Heck, I've never bought anything from Buy.com. Tricking people into clicking through to Amazon can work since they sell SOOOOOO much stuff that with 600 clicks you are bound to get someone who goes to buy something else there.

5) Are you promoting something that is overpriced at Buy.com or comes with free shipping elsewhere (like Amazon). No one is going to buy a laptop from Buy.com and pay shipping when it's available from Amazon for less with free shipping.

6) Are you promoting something super expensive that people shop around for a long time before buying? It's really hard to get sales for things like laptops that are over $1000, even with 600 clicks you might only get 1 if you're really lucky.

6) Are you promoting something that is out of stock?

7) Are you promoting something that very few people would buy from Buy.com? They sell shoes, but why the heck wouldn't you buy shoes from Zappos?

8) Finally, if 1-8 pass, and if you really want to know for 100% sure, perform a valid test. Pay a friend who doesn't live anywhere near you and doesn't share your last name to clear their cookies in their browser 100%, then click through your website and buy something from Buy.com with their own credit card shipped to their own address.

Good luck!

I doubt your sales are being stolen, it's very easy to have a high CTR and few if not 0 sales. If are you this concerned, give your AM a call and explain the situation and ask.