Obviously I don't know anything, but you need to be really careful with ads that say 18. Most underagers post as 18, and most professional sps with experience are not going to be just advertising on CL. So as a precaution, you should look for other ads on other sites, and just take a really hard look at how the ad is written.
If you do decide to book, let her know you will expect to see ID. She can cover her real name, but pic and age date should be visible. Other than that, the fact she offers incall is another clue, and you can decide if the building or area is a good one or shady one.