As now standard in the UK, usually the hot water inlet is on the left, and the cold on the right.
Occasionally, this is reversed and the shower may been fitted with a reversed inlet cartridge to cater for this. A few shower models from some manufacturers, for example Grohe, have reversed cartridges available.
A common example is the Grohe Auto 3000 shower. It's standard thermostatic cartridge is the 47450 000, but you will notice it's reversed version is also shown in the parts listing, the 47282 000 thermostatic cartridge.
99% of the time these showers are fitted with a standard non reversed cartridge, in this case the 47450 000. However, if unsure we would recommend get in touch with a plumber to confirm your supply orientation.
If you have any further questions, please get in touch with us.