A friend of mine is here on a tourist visa, and discovered he had 8 days overstay, as he forgot to do the extension in time.

We went to Phuket Immigration, where he was allowed to have the extension, provided he paid for the overstay at the same time.

I was under the impression, that once the visa was overstayed, it was impossible to extend it?

I asked the farang information officer, and he said it had always been like that.

Often immigration is accomodating and will extend after one pays the overstay fine, but they can indeed send you packing. The lenght of overstay will also be taken into consideration.

Indeed it has not always been like that - but recent experience being reported is that if you seem legit and pay the overstay they will provide. There are a lot of people who really do not know the rules and honestly make mistakes.