Open up a fifteen-year-old shower and you can usually tell within a minute whether it was built properly, because the failures are so consistent.
The most common one is tile set straight onto standard drywall or an unsealed backer board. It works for a while. Then grout hairlines, water wicks through, the board turns soft, and the framing behind it starts feeding a stain on the ceiling below. By the time a homeowner notices, the fix is no longer a bathroom job, it's a bathroom and a ceiling job.
The second is the pan and the slope. Water needs somewhere to go, and a shower floor built flat or sloped the wrong way holds water against the perimeter until it finds a way out. The third is penetrations — valves, mixers, niches, and anywhere a fastener goes through the wet surface. Those are the points a good installer treats as seriously as the field.
A properly built wet wall is a system: a waterproof membrane or a sealed board, corners and changes of plane treated, penetrations sealed, a sloped and tested pan, and only then tile. It is not a large percentage of the cost of a bathroom, and it is the entire difference between a shower that lasts twenty years and one that quietly ruins the room below it.
The other thing we check on every bathroom is the exhaust fan. In a Florida bathroom, a fan that is undersized — or worse, ducted into the attic instead of outside — moves your moisture problem somewhere you can't see it. We size fans for the room and duct them to the exterior, which costs very little at rough-in and is a nuisance to correct afterwards.
If you're getting bids, ask each contractor what waterproofing system they use by name and how they handle the pan. The specific answer tells you more about the finished bathroom than any photo of tile will.