what is the best way to help customer to avoid problem with new purchased products??

It is mandatory to understand what the customers expect from the product.
Than you have to show and explain him how it meets these expectations and promote the prodyct by other advantages of the product.
The most importat thing is to help him to avoid issues and problems.
It will be better to give him some advices about preventive actions and show tools associated to the products which can help him.
At least, you should give to the customer link, adress, Otline numbers in case off problems.

A very good question...
In the recent era due to the Product Innovations and changes in the technology a customer must be aware of the features within a product (Product Features), or in Service sector a client should be aware of the benefits they can avail.
Giving customers the Right product according to their usage is another way of satisfying customers and this will lead to avoid problems for the customer with a new product.
Explaining the after-sale Services associated with the product is a very good tool to satisfy the customers, sometimes the customer’s associate after-sale services with a product which will not be offered by your product.
So the best way is to explain the overall after-sale services during the purchase time.
Identify Customer Need as quickly as possible, most of the times the customer is looking for a product and the same product may not satisfy his/her particular need, i.e.
a customer is looking for an iphone and mostly he will be using Adobe Flash on that, but unfortunately iphone does not support flash player.
So if you just ask a simple question that “what will be the main usage for this product”?...
bear in mind a customer only worry about the main usage not the supporting features.
Give them a brief minute or30 sec at least about the benefits of the product, A customer must receive a brief about the benefits of the product, otherwise he wouldn’t be able to explain it to others and that can lead to dis-satisfaction when someone ask you the benefit of the particular product and you are not aware of that..
I am hopeful that this will be helpful.
Siraj

Point-to-point checking the product before selling the product to the Customer and if still the problem arises from the Customer, be patient with them and provide a faster solution.

Educate by simple explanation what the client can expect by using personal experience.
If you haven't tried it how will you promote it.

You must first understand the customer needs for the product and create the need for him and give the client all the details of the product technically

I think that the best way to do that is to understand the client's needs well before the sales process in order directed to the appropriate product to meet their needs, thereby reducing the likelihood of problems subsequent to the process of buying products that do not fit with the needs of the client

As today's technology is technologically advanced, we can do the following:-

1)  Determine the kind of customer intending to buy your product.  I mean, if they are belong to the educated or the uneducated section of the society, are they techno savvy or just ordinary customers.

2)  No matter what level the customers are, a small demonstration will definitely attract attention.  Therefore, if its operation, the type of care required is explained to the customer first-hand, even if they don't intend to buy the product, might prompt them to do.  This is a much better way than asking them to refer to the leaflet.

3)  You can also call them after a week, as a courtesy call, to check if they are satisfied with their purchase.

4)  Inform them that they can approach the customer service desk, in case of facing any problems and provide them with contact information.

Sell them what they need, not just what they want.

Best way to avoid this problem is to make sure customer's requirement is understood and a live demonstration is given to the customer where possible so that the customer has a clear idea how that product will serve the purpose.

Sell product as per his need &  provide quick training of new features & also provide them conact details of after sales deparment.   

understand the customer needs befor you make the sale.

understanding his needs and his resources are very important in delivering excellent service and  aproduct that meets the customer demand.

always ask