Vacations to Go is a reputable agency. I booked a cruise, many years ago, with them and had no problem.
A couple of things to know:
1. Their prices are the exact same that any other agency can give you.
2. Don't be taken in by their 80% off "90 Day Ticker". This is based on the "Brochure Rate" and the current price. No one pays brochure price on a cruise.
They are a legitimate agency and have good agents and some not so good. Just like any other. If you want to book with them, that's fine, but don't think they have a better "deal" than someone else.