>>>How do the big shops treat already replied stupid questions ?
Do you want your customers to get the type of service that the big shops give them?
If you reverse your attitude and actively welcome this type of communication, you may find you generate some extremely loyal clients.
Further, the problem you're experiencing may not be repeated requests for info, but it may be a general distrust of your company, i.e. they're checking up on you. IF so, giving them over the top service will lead to reduced service emails, once you've gained their trust.
BTW, my testimonials on my website are full of people talking about how we answer calls and provide service after they've not had that service at our competitors. If it helps, try looking at these people as 'people who are giving you their money'.