Taxis- I never take taxis but will need to in Italy

I almost always avoid taking taxis, but I'd need to take one to get from Rome to Ninfa's Garden- I would take the train from Rome to Latina Schola and then take a taxi for about 5 miles to get to Ninfa's Garden.

But, everything I'm reading about taxis in Italy pertains to taking taxis in cities like Rome, Florence, etc...

How do I avoid getting ripped off like in this blog:

https://www.aesme.co.uk/blogposts/giardinodininfa

At the station there are taxis, which are an absolute rip-off at 50 euros for a return trip (it’s a 10-12 minute drive) but there is no other way to reach the garden (it’s not a very nice walk) so you are a sitting duck.

Would I still use FreeNow App?

How do you know how much the taxi ride should cost? Rome2Rio says that the 4.7 mile taxi ride should cost around $17-$21. Does this sound right?

Assuming there are taxis waiting at the train station, there probably won't be taxis waiting outside Ninfa's garden. What do you then?

Do you wait to call the taxi after you are done? Some reviews on TripAdvisor talk about how their taxi driver never picked up the phone. Another review talks about when the driver showed up, there was already $20 on the meter which they had to pay in addition to the cost of driving them to their destination.

Pre-arrange the taxi to pick you up at a certain time? But, then that cost $60 for the blogger to do that.

Anything else I need to know about taking taxis in Italy?