Some guys want to protect themselves from legal liability. Each state is different. In New York State, it is illegal to provide "massage" service without a license. It is illegal to charge money for a "massage" service if you are not licensed. It is illegal to perform "massage" service in a location where it may be against the law. If caught violating any of these laws, you can end up in jail. Even if you are licensed, it may be illegal to perform the service in your home. You'd have to know the local zoning laws to be sure. Each building may have their own rules regarding work from home. If a legal case is brought against you, any ad that shows you asked for money in exchange for a "massage" service could be evidence against you. The legal onus for massage service is on the provider, not the customer. If someone has "Ask" in his ad, I would consider that person a bit more cautious. IMO, "Ask" may not mean scam at all. In fact, it could mean the opposite. Self-protection, which in turn can protect you.
I found this at a law site:
Because you need a license to give massages, merely an offer to give a massage or holding yourself out as an individual who can give massages is punishable as an "E" felony if you do not have a license to do so. While this offense is not considered Prostitution and a violation of New York Penal Law Article 230, the ramifications may be worse. The reality is that law enforcement, such as the NYPD, often pursues this charge as means to prosecute those people they believe are involved in Prostitution, but are unable to charge them with the crime of Prostitution or any of the other related offenses.