I think that you have assess the girls by a few simple categories to determine whether you would want to or can afford to date them or not.
Economically: Are you punching above your weight class? If you can't afford a civie in her league, you shouldn't waste your time. If you can afford whatever level of relationship you are seeking, then you need to ask if this is the person you want to invest your capital in.
Culturally: Is she ABC, KBC, or Americanized-in-general? How much do you really know about her culture and the expectations. If you are looking for fun, then you can just Google for some facts. If you are looking for a long term partner, you may want to live in that culture for at least a few months and understand the social norms. Whatever that norm is, will be what you are getting.
Sexually: Did you meet an innocent FOTB foot-rub girl, or did you BBFS/CIM and decide that you love how she handles your pipe? Her past with you and other clients will be at the center of your relationship unless you decide to move away and surpass her economic expectations. If she is a traveling provider, you may not want to relocate to her former client base.
Socially: Can you live in each other's social circle? If that is her "hand only" spa girls at KTV, it may be fun for a while. But can you take her anywhere in your circle? Will her presence in your life be damaging to your social circle?
If any of these categories pose a problem, you may just want to keep it transactional or FWB if you make it that far.
I do believe you can have a real relationship with a spa girl and get past the initial lies that protect you both. I think it is easier with simpler ladies that work at truly at legit spas vs. the girls earning $10-$20K a month from processing pipe. Just remember, if you can't transition from the transactional nature of a spa visit, it is not a relationship. It's an outcall.