Geography Postcards.

I wanted to give just two on US-390, as I like the card, but it's a Vatican card from NewYork. But system did not allow. So I tried to change after registering. Still not possible to change. How to do correctly?

I have updated this function. Some members complained about ratings being changed in revange. Now you can only update a rating up. For situations like yours you can now change a rating down only in the first two days after registration.
For the exchange mentioned above I have changed the rating as intended.

Yes, it is possible.
You log in, go to Postcards exchanges -> Received and then you could click on another assessment, confirm with Update, then upload the scan (if you haven't already done so) and Update again.

But let's not get into giving too many bad ratings... This is a bit of a "game", a pastime ! ;-)

Today I had 4, without explanation: my postcard was of the correct sub-region, the stamp was right and it was posted at the Post Office in that area. 4 !.. :-/

Ciao !