On a similar note, try to get a feel for each spa's ambiance to make sure it lives up to what you're hoping to find. For example, are you looking for a regal retreat, a tropical paradise or a rugged resort? Do you want to be exposed to a new culture or just stick with what you're used to? Are you looking to socialize with other spa goers or relax in tranquil solitude? Considering questions like these will help you as you read through the descriptions of different spas.
Also, most spas are coed but some are only open to one gender or another, so make sure you don't accidently book a vacation at a destination spa that's not going to let you in the front door. Among other potential restrictions are age, and depending on the spa, children and pets may or may not be allowed. There are spas that cater exclusively to couples and it's also important to note that sometimes spas are clothing-optional, so more modest people will want to keep an eye out for that.