I can't tell you how many showers I've torn out that weren't that old but were leaking. There's been a few where the customer knew something wasn't right and threw the contractor (?) out before even finishing the job.
The shower below was a beautiful travertine shower. Looked like a very professional job. Lasted about 6 years before adjacent walls began showing signs of damage.
There are many ways of waterproofing shower pans and walls. Tile can be set on greenboard or tile backerboard. All the showers I've torn out that were less than 10 years old (and often under 5) have something in common.; the pan was waterproofed using a liner and the walls were set on backerboard. It may be because of poor installation. Usually I can spot where the installer went wrong. But not always.
Why take a chance? Spend a little more, do it right. If you ever replace the shower it will be because you want a new look. All of the showers we've torn out that were 30+ years old have been hot mopped and "floated" cement.
The pan must be pre-sloped. I've rarely if ever seen this done where a pan liner was used. It's the code! Water that seeps through the grout and mortar reaches the waterproof barrier and if pre-sloped runs right to and down the drain through weep holes. Of course you must use the proper drain and not block the weep holes during installation.
Float the walls. Scratch coat, brown coat (the same way stucco is done).
Is water leaking into your house through your stucco? No. It's not going to leak through the 1"+ of mortar in your shower either.
It takes longer. It costs a little more. It takes a more experienced tile installer.
It's worth it!
I've seen liners installed all kinds of crazy ways. Folded in ways that hold water, staples and nails below the water line, corners cut, torn. I once removed a liner that was sealed to the drain with plumbers putty!
Hot mop the pan!
3 layers of tar paper and hot tar ran up the wall at least a foot.
It's not going to leak!
If you are using a one piece pan or tiling around a tub, there is nothing wrong with some of the quicker methods.
If you are tiling the walls and the pan then DO IT RIGHT!