Customer.Service@...
No matter how big or small your company is, customer service should be one of the first priorities. The only way to grow long term is to have content customers.
Having happy customers has not one, but two advantages:
A happy customer is not only more likely to come back; he is also going to tell others about your page. Unfortunately the opposite is true too: An unhappy customer is not only going to avoid your page in the future, but he will also tell others about that negative experience he had with you.
People are more likely to share a bad shopping experience, so that should be yet another good reason, to really go the extra mile.

How should a good customer service look like?

Answer your email in a timely manner. Be available
Checking your email once a day is not enough when you start an online business, no matter what size that business is. Email is fast and the web is world wide. The advantage that your shop is open 24 hours a day also brings the disadvantage that you will have to check in more than once in 24 hours.
The fact that you don't need to lock up this shop when you call it a day, and that it is still open when you sleep, does not mean that it takes care of itself and you are not needed.
Try to answer all inquiries within 12-24 hours - the faster the better. Again, think of you as a customer posting a question to a page that you want to buy something from.
How likely are you to buy something when you get an answer within an hour? How likely are you to buy something when it takes them a week to answer?

Acknowledge complaints ASAP
Everybody is fast to react on emails that tell you, how great the service was, but if you are not dealing with a happy customer it is even more important to react fast.
Customers who are unhappy usually feel helpless on top of their disappointment. This is especially true for web businesses where email is the only form of communication.
You can take a lot of the stress away from your customers if you react promptly and acknowledge their complaints. Acknowledging complaints does not mean that you can do anything about them right away, but at least the customer knows you are busy with the issue.
Example:
You are getting a question about a shipment that did not arrive at your customer yet. Let's assume it is after business hours, and you can not contact the postal service to ask where the shipment is. At least tell the customer that you ARE going to deal with the issue the next day during business hours. Then, when you have reached somebody at the postal service but they can't give you an answer right away, update your customer with that information. Maybe the postal service will tell you that they will have an answer in two days and they ask you to call back then. It is crucial to relay information like that to the customer. If you send out updates proactively, customers don't ask, they don't get pushy and - most of all- they don't get as frustrated. In the above example the customer would have gotten at least two update emails and would know that there will not be an answer for at least 2-3 days after his inquiry. Imagine the situation without updates: YOU know that there will be no news for 2 days and you figure, it is good enough to tell the customer once you have an answer. But how does it look from your customers' point of view?
He asks a question and only gets an answer 3 days later. Not a happy time for the customer.

Rules can be broken for customers
It does not hurt to have your Terms of Sale very well defined. It is good to have very clear rules for RMAs and returns. However, you can always stretch or break the rules you set, if it is for the good of the customer.
If a return is too late, you can still accept it even though you don't HAVE to. If a customer has to pay some extra fees for a service according to your Terms of Sale, you can still waive them. Little acts of kindness go a long way. Needless to say, it goes both ways. But you as the business owner can usually make the start easier.