I too change the plugs and fuses where applicable. Small repairs like flex changes if possible, and chargable if a job takes more than about 10 mins. If there are several repairs I will add up the time and charge an hourly rate or offer a fail and let them make an appointment for another day or trader to carry out repairs.
With regard to fuse changes, I tend to just do the obvious ones (table lamps etc) I will advise the client to check their user manuals for the correct fuse if there is doubt and always put this in writing (usually when I email documents to them).
One scenario to be wary of are fridges and freezers. On one occasion I replaced the fuse in an ice cream display freezer after measuring the operating current of 2 amps. I replaced the 13A fuse with a 5A. The next year I did a re-test on the unit to find silver paper across the fuse. The owner told me the fuse had blown and they didn't have a spare. I re-fitted a 13A fuse and told him to check his user manual for the correct value. Although the finger wasn't pointed I felt very embarrassed as they had lost all their ice cream when the fuse had blown.
As a result I now leave the fuse fitted to fridges and freezers and advise checking the user manual or look foe a plate on the appliance which states the correct fuse value. Another practice I have adopted is to always ask the client to check a fridge or freezer is on before I leave. A freezer full of rotting meat could prove very costly.