First of all, the USPS Priority Flat Rate box (there are 2 boxes) cost $8.95. According to USPS, there's supposedly a new larger Flat Rate box that costs $12.95. So I don't know where you got your $5 flat rate price from?
As far as FinishKare goes with their $5 flat rate shipping, do you actually think they can ship everything for $5? For some customers, maybe it costs them less than that but I'm sure for a majority of their customer, it costs a lot more than $5. So how are they able to do it? Simple. Add the cost of shipping into the cost of the product. AutoGeek does the same thing. Yeah, AG is usually a bit cheaper in the end once you factor in all costs involved, but it's not by a huge difference. Where AG is better than some of the smaller guys is the fact that you can buy more of what you want from one place, thereby saving on shipping costs. Even though shipping may be "free", in the end you're paying for it... it just doesn't show on your invoice as "shipping".
Also another thing people seem to forget is that the cost of shipping isn't just what it cost the person to ship it to you. You're forgetting about the person's/company's time to put that package together, the gas used to take it to the Post Office/Shipping center, the cost of packaging material, etc. That's why it's called shipping AND handling.
I hate paying for high shipping costs too and I'm also guilty for complaining. But the reality is that when doing business online, the product has to get shipped to you and somewhere along the line, that cost is passed down to the consumer. Unfortunately we live in a world today where most people expect to have their cake and eat it too.
IMO, I don't think enough people realize the severity of what this next recession might bring. I predict that it's only going to get worse.