Let's put it this way: Can you trust trade? Yes. Should you trust trade? It is extremely advised against. Can you organize or solicit a trust trade on the forums? No.
You indicate you know what the risks are in your opening post, but for those who don't - it is a trust trade that could result in loss of the money if the other party doesn't hold their end of the deal.
The other risk is even if the other party comes through on the deal, if their gold was obtained through rule-breaking means (such as RWT, for instance), the gold could be removed from the game by Jagex and you could end up without gold.
TL;DR - It's not expressly forbidden, but it's also not condoned.