How to keep "trolls" away?

Dear All,

I have a “playground site” on https://tmru.info

In the last days, I had about 50 registrations coming obviously from people whose intention is to “troll” on my site.

It would be a disaster if they start bidding because they will never pay if they win an item. (And they would probably flood my site with their fake auctions too since I would allow free listings.)

To prevent this, I thought to disallow user registration. I would instead place a “Registration” button. New users click on it and fill out a form with their names, etc. And I would create an account for them.

Would there be a more efficient (=requiring less work on my side) way to keep trolls away?

Thankx,
Attila