What is the most important for consumer,, the quality or the price of a good and why. how he can let his decision guide seller behavior ?

you can not ask this question like this this is depend on the market you are target and the product you will introduce to this market

IF the product is a new for the consumer he'll look1st on the price comparing with the price of the product he used to buy. If the price is better then he'll buy it as a trial and if he satisfied with the product quality he'll continue with it and if not he'll go back to the one he used it before. So both of price & quality is important, but coming step by step.