Trading safety precautions:

1.Dont ever trade from someone from trade channels.
2.If you really want to trade with said person, research his background.Scammer list are compiled everywhere.Search the keywords for 'scam' etc together with the battletag, and find out if hes clean.
3.If youre trading with someone from the forum, browse for a few pages about his past posts and threads in the forum.If there are many disputes or fishy threads(like multiple threads of unsold, cheap item), avoid.

That being said, I think its stupid to not play the game just because you dont have the nat's bonus anymore.
Like others said, you could always sell some of your gears and change your item and skill build.

I dont think anyone would sell legacy nat, let alone cheaply.

Ive known some ppl who sold their full gears to get rm profit and start from scratch and play again, now back farming act 3.
Maybe you dont have the motivation because you got scammed, but just imagine that the ring was something that you sell.
Only one ring is definitely much more easy to recover than full set, even for something as expensive as nat ring.