Taxi drivers adding on a few euros—is that just what is done?

I wonder if they charge for additional people or luggage?

Good point. We are two people and two suitcases and two backpacks.

There is a potential for all kinds of surcharges from extra luggage to additional passenger to a road toll. Could be taxes. If uncertain, ask.

Luggage, train/bus station pickup or drop off, minimum fares….

Fares and supplemental charges in Cordoba: https://www.pidetaxicordoba.es/tarifas/

Those can be surcharges because of different concepts... or they can simply be scamming you.

For example, in Barcelona, there are different surcharges that might apply and are legally charged at the end of the trip, from extra luggage to departure charges (port and airport), etc. I would imagine is the same in Cordoba and Granada.

These are all indicated in a large sticker on the side back windows that the passenger can read during the trip. This way you know whether these extra charges apply to you or not. Usually, the driver punches these charges into the ticket machine and when they print the ticket it's indicated there. It's a good practice to always ask for the ticket in case you need to place a complaint later on.

Here's what I found for Granada

https://www.lovegranada.com/transport/granada-taxis/

There is an extra charge for luggage: 0.51 € for each suitcase/bag
that exceeds 60 cm. Also, if you departure from Granada Train Station
or Granada Bus Station: 0,51€.

I’ve had drivers “round up” and self tip.