There is a lot of hype and frustration concerning COVID-19 testing. The three times I have flown this year, I have used Clinica Biblica to get my test. While is is a little more effort than the "hotel hype" of "sure, no problem, come on down, we will handle everything", it is certainly better than the OP's experience. I'll share a detailed review my experience at Biblica.
Background
Clinica Biblica is a private hospital in downtown San Jose, less than a c2mil Uber from SL, Castillo, etc. While not every employee speaks English, there us always someone available who can. They are open and providing service 24 hours a day, 7 days a week, 365 days a year.
Pre-Test
They accept reservations, but they are not required. If you have a reservation, you stand in one line. If you do not have a reservation, you stand in a different line. You pay when you get your test. There web site keeps be updated, but their English home page is:
https://www.clinicabiblica.com/en/ just scroll down and you should find a section for COVID-19. My advice is that registration will save you a little time on the say if the test.
Testing Location
Depending on the day of week and time of day, the test will be performed either in the hospital's regular lab area on the first floor or on the top floor of the parking garage across the street from the main entrance.
When You Arrive
You go to the testing location and take a number. For the garage, there are elevators as you enter. For the hospital, you go in inside and take a left. When your number is called you go to a checkin window. If you made a reservation, you will have filled in your basic info online (Name, Passport, Flight) they will still review it with you confirm. If you did not make a reservation, you still give the info. A reservation simply speeds the process. You pay your money and get a receipt. The cost of the different testing options is online. You now wait for your name to be called.
Testing Process
When a technician is ready, your name is ready and you go to a semi-private room and your sample is taken. A word of caution, if your name is Netgems, the sample is taken with a rectal scoop similar to a veterinarian testing your pet for worms. I'm not sure why, maybe they know something we don't.
Getting the Results
You can stay or go go. My results have always been ready within two hours. I usually go during slack times. You will get an email when your test has been completed. The test results will be a separate email. If you elected to stay at the hospital you can get a printed copy at the lab. I think the emails are sent when their staff have time, I usually get mine before 4pm. If you need it sooner, you can call the hospital main number after you get the first email (again on the website) and ask for the lab. They can send you a copy while you are on the phone.
As a last note, the OP's caution is well founded. Customer Service at all Costa Rican businesses has become worse. I hope that things will return to their pre-pandemic norms. I'm not rationalizing bad service. Hopefully, any owners out there read and heed the last line of the OP's post. If not, they wont be in business next year. Nobody wins in that scenario.