I want to know customer's opinion about salon and spa locations. Would you suggest using a multi-star rating for the review, a single heart to "like" a location, or both of these systems together?
I would suggest using stars only because users can see whats the rating from 1 to 5 and make a decision about the particular spa location.
If there are only likes, a newly added location may be better than the rest but won't have as much likes as it's recently added.
Avoid adding both, rating and likes because they will lead users to confusion thinking which should they look: likes or ratings, which is more valid, etc.
Think about the factors on which something is liked or 'rated'. The more complicated things become, people prefer relative grading. Heart is primitive. It is a binary choice. You either like Vanilla Ice cream or you don't. Not all parameters are as simple as that.
Have a look at the things that usually have hearts. Those are binary choices. Twitter recently moved favorites from single star to hearts. It is 140 characters in length, you either like it or you don't. Other possible use of a binary choice is something like a bookmark system. A places you want to go, you mark them.
When a consumer is grading an establishment like a salon or spa, from Hygiene to staff courteousness, there are many factors on which she can rate it. On the other hand, when a consumer wants to select a place to visit there might be many aspects helpful for making a decision. For this purposes star system is much more helpful and a norm.
Look at Google Places and or Zomato eateries. Their grading systems definitely include multi-step stars. This has also helped in shaping user's mental models. A user might expect more information which is provided by a multi-step rating system.
A combination can work too. Along with giving a star system based review, you might want to ask user to recommend or not. A recommendation is a binary choice. Your system can ask for user to recommend a salon or spa. However, this is over an above a multi-step rating system.
As everything UX, it all depends on the context. Your information is incomplete, but let's see some typical cases:
You want to inform people and nothing else
In this case, a rating system -whether stars or something else, this is a different question- will be the more appropriate. Basically you'll be creating a list with community driven ratings. You don't have any preference for any item in the list, so you leave it all to the community
You want to charge for listings
In this case, you should use hearts (or anything else but ratings). Just imagine the situation: someone buys a spot, pays for the advertisement and then they get 1 star. Literally, they would be paying you to destroy their business. As simple as that. So, you should use a positive rating system, meaning by this a rating that has no negative connotations. Please note that hearts is a somehow confusing icon, since it's usually used for "favorite" rather than "liked" or "loved", although I admit the metaphor may work in context. However, you could try something else, specially fi you're after branding
You want to "keep it clean"
Here, you make the reviewer take responsibility for their actions. You can require the user to sign up, you can require the user to ACTUALLY be an use for those services, or can use an external rating system. For example, you can use Facebook so you know users are (mostly) real and willing to provide their name/profile. This will give you access to their "like" system and you can promote your service at the same time.
there are other options you might try, but we'd need A LOT more information that what you gave. In the end, it all comes to your needs. And even then, an option might look great on theory but testing shows it's a failure. So, as I always say: "test, test, test"
In general, for places and locations we use star, like in "5 star hotel" and heart for products and services. It is not a rule, but it is a good abstraction from real world to digital. So in this case, I Suggest stars
It's more appropriate to use stars when it comes to locations. Hearts can be use for feelings and customer experience.