Try to figure out away to pick the basket that allows you to create more baskets. I will not get involved in a business in which I am dependent on a few clients/customers for the majority of my income.
Pretty much the rule of thumb I live my life by.
If I loose this customer how will it affect my life? You have major problems if the thought of loosing that customer/client/website makes you more than a little uncomfortable.
Just about any business can protect itself by diversifying their income streams.
I know what you mean and this is kind of how I've always been focusing my projects as well. Thankfully I don't do much client work or anything so I'm not in a bad situation in that sense, but other than that I think I get your point.