If you are concerned about flooding, the first thing I should do is simply ask the owner about flooding history. The second thing would be to check flood plain maps for the area in which the property is located. FEMA has maps at : https://msc.fema.gov/portal
But this is not an easy system to work with. You probably will also find online maps hosted by your local government.
To answer your original question: the presence of a sump pump really means nothing except that there is a system to protect the home just in case. You may remember from news reports last September that we had a very unusual storm here in the Boulder CO area. Many people who have sump pumps reported that they had never before heard the pumps working. They were, however, very glad that they had them during our so-called "1,000-year-storm."
The saddest stories came from people with pumps that failed to work. Usually this was because they never checked to make sure the pumps were functioning. A quick and dirty check is easy to do. If you manually raise the float and it moves relatively easily to the level where the motor turns on, (and if the motor turns on, of course), then you probably are okay. If the float does not move easily, or if the motor does not turn on, then repairs may be in order.