According to Home Depot's website, you can purchase a wallplate for a receptacle or light switch for $0.22. Very often, I find myself writing inspection reports with multiple receptacles and light switches missing wallplates. I don't think anyone can argue that an uncovered receptacle is safe. VERY easy to install, VERY cheap to purchase, a VERY good investment to ensure safety and another VERY easy way to avoid a "nit-picky" inspection item!
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Tacoma Home Inspector

Your recommendation is dead on. I think sometimes sellers just don't want to deal with the little things though it can make a big difference in the buyers' perception.
Also hiring the right inspector will help with getting a fair report also
Why won't you put a outlet cover on? Again, I always say this, I don't understand people.
22¢ for an outlet cover? Holy where-am-I-going-to-get-that-kind-of-money, Batman?
I went out on an inspection a couple of days ago and every outlet and light switche was missing the cover. Probably about 50 of them. 50 x 22¢ = $11.00! Who has that kind of money? LOL
I agree, there is one missing in at least half of the houses I list and they cost under a dollar, plus it is dangerous as well. Wish all the fixes were this easy and cheap!
Once the outlet covers are purchased, who is going to put them on? Who keeps a scredriver in the house? And think how much time it takes. Those homeowners cuold be, like, watching sports or having a brew, during the time it takes to put an outlet cover on. And light switches, too!
When I list a house, this is one of the things that I look for and recommend that the seller remedy it before the sign goes up.