When it comes to complaining about products that don't sadisfy my expectations, I prefer to complain in person.
Altough a lot of people may prefer to complain in writing, I think that complaining in person is more efficient.
Writing a letter or an email can hepl you to structure better your complain but you are clearly missing the direct contact with the responsable person.
Complaing in person is the easiest way to talk directly with the person in charge instead of writing a letter and don't know who will answer you or even if you will ever receive an answer.
For example my sister bought a laptop that was defect. She wrote a letter and didn't receive an answer. When she finally went to the computer shop to complain the service of the customer care solved the problem immediately by giving her a new laptop.
Also they felt really sorry because of the inconvenience they caused my sister.
Another reason to complain directly in the shop is that you can explain better what the problem is. While you are talking with the responsible persons, they could ask you new questions that you didn't think about in the first place.In this way they save time to understand what the problem ist and solve it.
Once my cousin was working in a call center for a big mobile company, where they were also responding to emails in which customers described their problems with the products.He explained to me that the avarage customer doesn't have a clear idea of how to explain the problem in the right way so that the experts can not solve it quickly. The results are a lot of useless emails and a lot of wasted time.
All this could be evaded going directly to the shop.
Even if in these days a lot of shops are working online with e-commerce and the customer service is just an