What a sales person have to do when targeted customer is not willing to buy it's product. even he has tried enough?

Not to be pushy on the customer and inform him of new stock arriving soon . maybe next time the customer will be convinced.

Be positive but not too pushy and pleasant in a diplomatic manner convince the customer honestly so we can gain their trust in personal level first, it works in most cases.

We may possibly try everything we could in our best of knowledge how we want to be treated as customers also, from this point of view I would definitely would give them enough portion of "testers or testing the product in the minimum size after we try to sell them the product in the sale price.

 Coming back asking for more hopefully and follow up with the customer how did they go with the product and their feedback having access to permit of their personal contacts perhaps and leave our business contact for more assistant in future reference in giving them my name and contact to help, assure the product is working for them and provide them with more selection of new coming product, etc.