What's not entirely clear to me right now is whether trades need to be direct or whether there's some kind of credit system.

If the trades need to be direct (e.g. two people trade something with each other one-on-one), that severely increases the number of users you need to be successful. (Versus getting a credit and being able to redeem it with someone that offers something you want.)

To answer your question more specifically though, I would consider focusing on a niche at first. Right now #barttar is for everyone which makes it very difficult to market and people to identify with.

Let's say it was focused on trading coders and designers trading their skills. Then all of a sudden tech and design sites will take notice. It becomes relevant to their audience and so they are more likely to cover it. You will also be able to use more specific language on your homepage when a designer or developer comes across the site, they feel like the service is specifically for them.

Have any trades happened yet? Which types of trades have been the most successful?

Yes a lot of trades have happened. Services related trades have been successful.

Could you pinpoint it even more to what kind of service related trades? For a marketplace like this I really believe it's all about cornering one specific market and growing it from there.

The trades happening on barttar are all direct. I plan to introduce some kind of alternate trading currency. So should you want a trade but can't offer something, you can use the currency to trade instead

It's been mostly coding, design but also people sharing books, cards have been good trades too

I agree with Marc. If you try and target everyone and your not a GIANT, (like facebook, twitter, etc .... ) you will end up missing everyone. At the moment, you're saying "We solve all sorts of problems for everybody". You need to say we solve this problem for this type of person.

Choosing a niche makes marketing much easier.
Because you know where your customers hang out.
Zone in on an obscure community which can help each other out.
Just an example, but if you zone in on "saxaphone players" you can then think where do saxaphone players hang out?

They read the same forums, they go to the same conferences, they follow the same people on twitter, they all watch the same you tube channels. If you're providing a service specific to a community then it will spread through that community like fire.

Your site is of very good quality. And I really like the idea. Good Luck.

Alright, Thanks Harry & Marc. Will do that