What to do if I think that all other players are attacking?

Definitely do not trade, you would lose your wager. Sometimes attacking as well is a good option, as everybody will get a similar share of the loot and the game will move to another round. Playing defense often makes more sense, as you can get a special card based on the Tragic Hero rule. If used well, the special card can bring more when used successfully in the game.

Importance of the last round

Last round of the game is often decisive, as some players might wager all their coins in attempts to win the game. Even if you are behind the leading player, a successful last round can often lead to victory. It therefore makes sense to keep a special card for the last round – it may make a difference between winning or losing the game.