For what purpose are you cleaning the mark? Visual appearance, hygiene or odour issue?
Or more correctly, put those in order of importance according to what the customer wants.
some things you'd need to consider are the overall condition of the carpet, what the face fibre is, whether this was liquid
which may have soaked through, have they attempted cleaning it with water (most likely and this may have allowed the substance to migrate deeper and wider underneath than the actual mark on top)