If its an old stain dont waste too much time with it you will have limited success but may lighten the area around it which if its an awkward customer may become your problem.
Many variables- initially pee is acidic then changes to ammonia (alkaline) over time chemically 'burning' the fibres/ dyes. This stain wont just flush out its not soluble , it will need either reducing agent ie sodium metasulphite stuff ( as mentioned sray & go ) etc or oxy agent ( peroxide based ) spotter.
Knowing when to try , what to try , how much to try & when to say no comes with time & experience.
Mike