Let's say if you sell starbits/starpro and giveaway Hive to others people. Is this a ban?

Only if those other people use that Hive to boost their RSG game

If you convert it to DEC and giveaway DEC. Is this also a ban.

Only if those other people use that DEC to boost their RSG game

If you buy a card with DEC and giveaway this card. Is this also a ban.

Yes, unless the card is involved in a whitelisted giveaway

This is too much. I think. RSG is trying to restricted all from of giveaway.

The exceptions for giveaways are pretty clearly stated in the TOC and this post, I thought.

What about P2P? How can you know it is gifted or not.

You can't, so be careful with P2P and keep a history of your conversations if you think that P2P trades involving RSG assets might run afoul of the rules.

If I send my swap.hive to @hiveupme can it also consider at a gift.

I don't think that account plays RSG—it looks like a curation system, so you should be fine. If that account used the SWAP.HIVE to buy RSG assets it'd be a problem.