I'll agree with everyone here, for feet you can always get a bowl of water and some nice oils in it to soften skin and clean the feet up / pamper them, or use a footspa, which gets rid of that problem.
I've not treated anyone myself who hasn't made the effort, been lucky so far I guess, but wondering, if you do aromatherapy or something which uses oils you could remind them that the effects of the oils will be heightened if you leave the oils on overnight, so it's often a good idea to grab a shower before coming for the treatment itself .. to let the oils do their thing to their full potential..