In general, the metadata values of your product can be trusted.
Maybe this topic is helpful to you to clearly distingquish between pixel spacing and spatial resolution:
I have read this topic several times but I don’t understand how determine precise dimensions of rectangular pixels in a initial SLC image.
I think that I must use pixel spacing and not spatial resolution but maybe it isn’t correct, do you help me?
Can you give a little more information on how you want to use the data and why the exact pixel spacing matters to you?
Ok, I would write in my document that the pixels represent rectangular areas in the SLC images and that their dimensions are of…
then I’d take the values from the metadata.