Try to get free shipping, that way you don't get an additional charge on top of the sale price.
If you decide to sell stuff then be aware you only make about 8 dollars out of every $15 you sell due to ebay's charges and shipping. Your time spent putting stuff on there and managing stuff is enormous. One of my friends spends about 12-15 hours per day adding stuff and shipping stuff.
Since she's selling small stuff she doesn't make much money off each sale.
So if you see something you like then you buy it. Unless the person misled you and sold you something other than what was in the picture OR it was a different size than what they showed on the add please don't send stuff back. They lose their ratings or something and it cuts how many items they can post and how much they make on the rest of their items.
It's a big deal to return something and request a refund.
Now I did see something the other day where someone bought a leotard for their child, they needed a child small. The person selling the leotard looked at the tag and it said small. The thing is, most dance clothes say xsmall, small, medium, and large on adult items and child x-small, child small, child medium, etc... OR they say child 4-5, child 6X-7, child 8-10, and so forth. So when the lady got her small leotard in the mail for her little 4 year old daughter she did indeed get an adult small leotard. Of course the seller didn't realize they'd made a mistake reading the label so that refund was made. But the seller still got sanctioned by ebay.
If a vendor on ebay has been there a while they're probably okay to do business with. If they are selling things within your price range and the clothes look cute then what's the risk? If they're stained or missized or something you can send them back and get a refund.