Nobody will ever let you MM without a healthy amount of feedbacks. Generally, a good way to build a reputation is as follows:
1.) Buy sponsor. This does not mean you are trustworthy, but people will be more likely to trust you because obviously you aren't going to scam someone for $10 after dropping $50 on a membership title. You could, but you'd be downright stupid.
2.) POST. Be active in the community. Get your name out there, give people advice, maybe learn a little java. Be useful. If people recognize your name, and you aren't just some nobody with 30 posts and 0 feedback, they'll be more likely to trust you.
3.) Buy stuff. A good way to get feedbacks is simply buying and trading a verified trader like Divica (personally, I'd never use yoloswag69420. He's trusted but he's kind of a tool in my opinion. I've sold him $20-30 in gold and he's pestered me for a feedback, which I provided, and then ignored me when I asked him to reciprocate. Divica, on the other hand, is wonderful with leaving me feedback despite not having to).
4.) Sell things for less than they're worth. Buy a couple of membership pins for 4m from a trusted dealer, or from the store. Then, sell them for a little bit under the market price. You'll end up with satisfied customers, get your name out there, and get feedback.
5.) Be willing to use a middleman, or go out of your way for your customers. Let them haggle your price down, OFFER a middleman (instead of having to be asked), etc. Be aware that NOBODY will trust you, and you aren't entitled to trust. If you want to gain a presence on the forums, be willing to risk it for the biscuit. You might get scammed a few times, but it's the name of the game.
6.) Once you have sufficient (20+) feedbacks, start selling goods at slightly below market price. Start selling your gold at a good price. You'll have a healthy amount of trust and you'll make a fair amount of money, gain customers, and gain feedback.
7.) At 50+ feedbacks, you're basically a solid member of the community. At that point, perhaps start offering a middleman.
Always make sure to MAINTAIN your presence in the community. Don't post random shit on 100 threads a day for a week and then go missing for a month. Keep up with whats happening in the community, make your opinion heard, give good advice.
It will take a LONG time before you gain the trust of the community. It's a journey. If the community is something you truly enjoy, then keep at it, and you'll gain a presence with some hard work and dedication.