The site is continually growing with new people joining every day. Yes it may seem low, but CAG is a massive site compared to Leaptrade. It's also still a fairly new site, and it takes time to grow. It's a reliable site, especially with their Leaptrade guarantee, which is a simple way of saying traders are covered if a mistake happens during the trading process.
If you feel a game is priced too high, they do price match games if you ask them. Also, some newer games wont make it up right away, but people do trade in newer games eventually, just takes time, and there is usually some new games listed once in a while. Remember it's a game trading site, so not every new game will be available.
Anyways, hope that helps you out a bit. It's a growing site and it will get better.