It is very important that buyers can see that you are a trustworthy seller. The first thing that they will look for is your feedback. I would suggest that you buy a few things from eBay before selling anything. This will not only increase your feedback (as alot of buyers are put off by zero feedback) but allow you to get used to how eBay works and investigate how other sellers do things. The quicker that you can build up your feedback the better, as you will find that you can charge higher prices once potential customers can see that you are trustworthy. It is best to list some less valuable items first, as once your feedback is over 10 people will be happier to buy from you.
Another way to build up trust is to make sure that you respond promptly to customer enquiries. I will often send an enquiry to a seller just to find out how quickly they respond so that I get an idea of how efficient they are. Also make sure that your responses are as helpful and polite as possible without being pushy.
Make sure that once your item sells that you send out an invoice as soon as possible. This will not only show that you are efficient but also means that the buyer is more likely to pay more quickly, which is always good for any seller!
Once you receive the payment, send out the item as soon as possible and in new packaging. It is best to buy packaging in bulk so that you can get it more cheaply but remember that you can add the cost of it into your postage charge. I find that my customers would rather pay a little more and get good packaging. Remember some buyers also sell and so may like to reuse the packaging themselves.
When charging for postage make sure that you do not overcharge. It is against eBay's rules to do so, is annoying to buyers and will certainly encourage negative comments and spoil your reputation. I do not think it is unreasonable to charge between 25p and 50p for packaging.
Make sure that your parcels are as professional looking as possible but add a personal touch. I put the addresses on a label but hand write it, but have an address stamp for the return address. I put in a professionally printed compliment slip but handwrite a freindly message on it.
Lastly make sure that you deal with any complaints politely. Remember that if you are a business every customer is entitled to return their items even if they are not faulty. Make sure that you make it clear to customers how to do this within your terms and conditions. If an item has been damaged in the post it is up to the sender to claim compensation from the post office. Therefore you need to agree with the customer whether they want to return the item to you and get a full refund or send you a photograph of the damage and get a partial refund. Once you have sorted this out then claim compensation from the royal mail. I always make sure I apoloise if items do not arrive or are damaged. It is not my fault but it makes the customer feel much better!