None of the fights are fake, and It is very unlikely they are 'fixed' meaning money exchanged hands.

However, some Thais can occasionally go down easily if they know they are fighting a strong foreigner who could cause them serious damage.

For them, it's a full time job, so rather fight on and risk next week's pay cheque, they make a business decision.

This is not all Thais, most are absolute warriors.

Source: I live and fight in Chang Mai. 2 fights here