It's best to try to keep the nest boxes as clean as possible, so the eggs stay nice and clean anyway. Check after dark to see that the hens aren't sleeping in the nest boxes and pooing in them overnight. If you find one or more of the hens is sleeping in the boxes, put a big plastic flowerpot in each box before they go to roost, and remove it early next morning before they get up. Or go down after dark and lift out any hens that are in the boxes, then place them on the perches. After a few nights they will learn to perch properly. This is important when starting with new pullets, who will probably have been raised in a barn with no perches, and have to be taught what to do.
Some nest boxes can be fitted with roll-away inserts, so the egg rolls down a slope into a collecting space as soon as it's laid, thus reducing the chance that a hen will touch it with dirty feet.
Also, poo pick the coops daily, so they don't have to walk in poo on their way in to lay. Aubiose is best in the coops as its so easy to poo pick, it literally takes only a minute to pull out the overnight poos and collect them in a bucket for the compost heap. In the boxes, a nice deep layer of Aubiose or wood shavings or similar bedding will help keep eggs clean. Not straw as it's not absorbent and is hard to keep clean, and not hay, as it may give them respiratory problems and also isn't easy to poo pick.
If you're selling your eggs, I believe its illegal to wash or wet-wipe them. When eggs are laid they have an invisible protective coating so bacteria won't penetrate the porous shell.If they're washed, this is removed, and its possible that bacteria will get through the pores in the shell so the egg won't stay fresh for so long. That's also why it's important to incubate eggs which are naturally clean, because if they're dirty and then washed, its more likely that the chick may be infected and not hatch properly.
When I get a dirty egg, I do wash or wipe it if I'm making boiled eggs, where you don't want to see poo on your shell at breakfast, but I only do it just before boiling it. Some hens are worse than others - I've got a Columbian Blacktail who is the best layer of all of them, a large brown egg arrives daily - and she nearly always manages to muck it up!