So there's commission - is it expensive?
Firstly, remember, you don't need to pay anything to start with. You can advertise what you do, accept offers to do things, or even do a "swap" with someone - all for nothing. Commission is only due when you spend Barts.
As to the commission, it's not expensive, it's really low! Anne's total commission on the payment of 20 Barts, was 50 centimos. And for that amount, she found someone who could do the job, and perhaps found comments from other BartPeople, about work that Billy had done for them. This was quite useful for Anne, because if Billy had paid for newspaper adverts, then he would have had to put up his fees, to cover his advertising costs. With BarterwithBart, his advertising cost was - zero. And Billy could have found comments from others who had done work for Anne, and people who Anne had done things for as well.
So 50 centimos was taken from Anne, as commission. Where did that come from? Well, to spend money (and note, not to advertise your services, because that is free), you have to pay commission. And it would be silly, time-wasting, and expensive (you know how much regular banks charge) to collect 50c from Anne.
Well, you know how Pay As You Go mobile phones work? You charge your phone with as much or as little credit as you want. It's the same with BarterwithBart. Deposit a minimum of 5 Euros into your Europot, and that's where the commission comes from. And if you should use it all up, you will be sent an email, to remind you to top up, which you can do direct from your computer. If you choose not to top up, you will still be able to advertise and receive Barts. But you won't be able to spend any until you top up. You won't be able to contact anyone about barters, but they will be able to contact you. Just like a mobile phone. But less expensive.