I agree, you need to go with your gut feeling. I am using a Town Car service for the first time this trip.
I chose Cartier because they had very positive reviews and they answered my e-mails very professionally and courteously. I have had great interaction with them and have recommended them to family even though I haven't actually used them yet. I feel very positive.
When I see people post a negative review, I take it with a grain of salt. Everyone has different criteria and different expectations. I see people post scathing reviews of resorte because they didn't get towel animals and I see people post positive reviews, because even thought the room wasn't what they expected they liked the service or the decor.
Some people tend to see the negative in everything and some tend to be more positive. Until I have a bad experience or hear from someone I trust 100%, I will make my own judgements and not let myself be swayed or get nervous.
Every business is going to get a bad review or have an incident happen that's beyond their control. It's how they deal with it and how they treat you as customer that truly matters.