I would think that by having this requirement, it keeps down the chance of getting scammed.I personally feel safe buying things from the people here. If anyone could come on here and offer to sell the first time, then you would have to worry about if you will get anything for your money.
I don't think the requirement is that hard to achieve. I wasn't even trying and noticed that I had achieved it. I don't even know how long I was a regular before I noticed.