Wraps have come on in leaps and bounds technically and are far better than they used to be. The choice of material is now huge. Unfortunately their ease of application means there are very many muppets out there that have set themselves up as wrappers. The material itself is quite cheap, as are the tools to fit it, a tempting combination for the chancer.
In just the same way as there are good detailers and bad detailers, the same applies her, so do your homework and work on proven recommendation. It's down to training and experience. The car has to be prepped. To wrap a car correctly involves a certain amount of dismantling and the time to wrap a car is the deal breaker. If anyone tells you a car can be wrapped in a day then walk away.
Expectation is also important. A colour change wrap will not hide the colour of the car in the engine bay nor in any other exposed none body areas.
A good wrap will be a couple of grand or more, so do yourself a favour and get any dents sorted beforehand, as they'll show and will even be exaggerated depending on the wrap colour.
As for not being able to polish a wrap, this is nonsense. It takes polish very well, so you can achieve just the same surface sheen as you would with a painted surface, assuming the polish is applied correctly.
If there's any one rule of thumb before choosing your wrapper, remember the guy is going to be all over your car with a scalpel.