Your short question focuses on one of the most complex areas of negotiation.
Interests are 'why' people want what they want.
You must certainly have a clear idea of what price is appropriate given your own costs of acquisition, manufacture, preparation, overheads, etc. You need to find out the value of that item or those items to the client. One thought is to consider each negotiation as designed to yield a 'package' rather than just a 'price'. You also need to ascertain whether you are dealing with someone only one time or are beginning or continuing a relationship. When you indicate that you are offering 'quality products and services', one question is the cost-benefit analysis of any given transaction to each party.