Established business customers get full credit with me on new systems. As others have stated you are just shooting yourself in the foot when you don't extend net terms to businesses.
Your avg. home user must pay 50% the cost of the system up front at the time of order, the rest to be paid on receipt of the product.
I also make good margins on my custom builds. Yes, this means I don't sell a lot of them, but that's ok, the ones I do sell are actually worth my time to sell, not a waste, and I'm not worried about the slim markups that many get while trying to compete with the big boys. I never try to compete, I only look out for my business interests.
If a customer doesn't like my prices, I'll recommend something else plain and simple. If they want to know why my prices are higher, I'll explain and they usually understand that A. I cannot compete with the big boys regardless, B. I'm selling them better quality components, and C. my support is local and in their own language!
Most people who are only looking out for savings when buying a PC, you don't want them buying a PC from you anyway. When I worked at Gateway around the time that the sub-$500 PC came out and put PCs in more lower income homes than ever, we noticed a trend in that those who went after the cheap PCs were generally more difficult to work with in terms of support; meaning they were stupid, and therefore very needy when it came to PC usage. Not saying that there is a direct correlation between income level and intelligence, (also keeping in mind that these people had no prior experience with PCs) but looking at the numbers from our point of view, well, it didn't matter because for one reason or another you didn't want to work consumer support after the cheap PCs hit the market. Those in business class support where the cost of the PCs were significantly higher didn't have the issues with clients that we did.
So in my opinion those seeking discounts over quality are more likely to be your problem customers for one reason or another, intelligence or mere lack of experience regardless, they will call you for every little thing.
On the other hand, those who are concerned with quality over price, then I accommodate them happily.