Buffer doesn't compete for San Francisco talent and that's OK. Of their 85 employees, they have 1 engineer in SF. Maybe that person isn't making bank. But the 3 persons in Barcelona appear to be. Average engineer salary in Barcelona is $44K and Buffer is paying $100K+. Good for them!
https://docs.google.com/spreadsheets/d/11s9VSyf4yaYUsqBKLaVH...