What is your target market for "making money"? (large or small customers). If you expect to make real money on large customers then negotiating a special relationship where you actually "get in bed" with the large customer to learn their requirements will really accelerate your product development focus - ie. give them even more of a price break IF they commit resources to help direct your product.

The reality is you WILL have problems with this large customer and you want to lay the groundwork for a give and take relationship where you will both be winners in the long run.