Fair to refuse to pay for painting?

[Marci Stein]

I have a SFH which has been rented by same family for 10 years . I inherited the tenants when I bought it 4 years ago .

Even though they’re very messy , They always pay on the 1st of each month.  Now they want me to pay for house painting, which hasn’t been done in a decade. 

I’m reluctant because even though I’ve raised the rent each year ,  it’s still $150 a month below market . 

Is it fair to refuse to paint? What’s the usual protocol regarding painting when there are 

long term tenants ?

Thanks!