Most people looking into solar believe that the more panels on your roof, the better. While you do want to maximize your roof space to generate as much power as possible, too many can generate more power than you need, and, due to the way conventional Net Metering works your utility will not pay you for the extra power you generated at the end of the year. You will want to pick a solar installer that will give you a realistic quote based on your electric bill, shading, and roof facing direction.
Many solar energy salespeople make commission based on the number of panels or killowatts sold. This incentivizes maximizing the number of panels installed per customer, so certain companies, in an attempt to make more money, will install more panels than is necessary in order to zero out your bill. Shaded panels and panels packed in on west, east, and north facing roofs are often the result of a salesperson looking to make an extra buck.
You'll want to choose a solar company that isn't looking to take advantage of you. That means they're not going to install modules where there's alot of shade, where the roof is north facing, or where the roof is too steep for the panels to absorb sunlight. A proper installer will analyze your bill and roof orientation to optimize installation such that you aren't producing more power than you need, and don't have panels that are unneccessary or shaded.
The number of panels you need is based on two factors: the available space on your roof and the size of your electric bill. A good installer will not take advantage of you by installing modules where there is a lot of shade or a poor north-facing orientation on a steep roof. Along the same lines, your installer should analyze your current electric bill and recommend the number of solar panels that will get you close to a zero bill. Your installer should also guide you through the options for different levels of solar panel efficiency, module electronics (optimizers or microinverters), and changes in your future use of electricity (such as an EV or energy conservation measures).