In fact , there are dozens(hundreds?) of maid out there who don't mind doing "extra work" for "extra pay".

"Susan, master needs you for a job.blablablah...."
"Master.. But this is not good, I scared madam find out.. and agency also... But, hmmm.. you pay me for this?"
"Susan, yes, master pay you this time, everytime and anytime I need it."
"Master.. hmmm.. you pay for the CD also can?"
"Susan, yes, room and CD paid for!"
"Master... hmmm.... fuck me!"

And so the deal was done. The ones that appeared in the new are the unwilling ones, and unfortunately the masters thought they could force their way by intimidating, abuse, and worse, thought it should be FOC... sigh..