I can't speak for others, but I've now bought and sold with TransformerLand.com and have had nothing but great experiences each time. They've even alerted me to some upcoming preorders.
They're doing a really good job over there! Highly recommend the site.
Tip for consumers: Read the descriptions for each toy you're interested in. It tells you exactly wht's being sold. Read the site as well - It says they have small children and may take a bit to get back to you, but I've never been disappointed.