Flight to Sofia - is it mis-selling?

Sandtree

mattyprice4004 said:

You are responsible for making sure you're eligible to enter a country, that's not the airline's job. 

The airline does actually have a duty to make checks but its at the point of check in not point of sale... in the gap between the two requirements may have changed, visas obtained etc. Some countries fine airlines who bring someone to their borders that doesnt have the right to enter.