Here are some things to look at when hiring a Photo Booth Company.
What kind of Booth are you getting?
Is it a camera on a tripod or professionally built photo booth?
What kind of Camera are they using?
What kind of lighting are they using?
Do there pictures look nice and clear?
What kind of backdrop choices do they have?
Does their setup look professional and add to the ambiance of the party?
What kind of printer are they using?
What do their templates look like?
How fast will they post your digital pictures after the event?
Will they provide you with excellent customer service?
What kind of props do they offer if any?
Will your booth be up and running by the time that you want?
Will they send an inexperienced college kid to your event and pass them off as a professional?
If something goes wrong at the event, would they know how to fix it?
Do they understand photography and how light works?
Do they have liability insurance in case of an accident? Some venues require vendor insurance.
Who have they worked with in the past?
Are they capable of handling large events with 500 + people or do they mostly do small backyard parties?
These are just a few questions that you should be asking before hiring a photo booth.
I have heard recently from talking with people that there some photo booth scams out there offering a ridiculously low priced rental price. They ask for all the money upfront via a PayPal account, and then take the money and run.
This also goes for hiring photographers too. I have heard many stories about photographers not delivering their images after an event, even after a year.
Here is an article to read about why you are doing yourself a disservice by hiring a cheap and low quality booth.