Is it ok for me to ask viewers to take their shoes upon entering my home, which is for sale?

My house has been put on the market for sale and I have had quite a few visitors viewing it. I have noticed that most of the viewers don't take their shoes and in most cases don't even offer! The times that I have asked for them to take their shoes off, they seem absolutely flabbergasted and they seem to... show more My house has been put on the market for sale and I have had quite a few visitors viewing it. I have noticed that most of the viewers don't take their shoes and in most cases don't even offer! The times that I have asked for them to take their shoes off, they seem absolutely flabbergasted and they seem to put in a bad mood! I just wondered if anyone else had similar experiences or people's opinions on this. This is still my home before it sells with my property in it. Surely it's not too much to ask to take their shoes off? Especially when I've cleaned the place up and down prior to their visit.
Update: Can we all just bare in mind in live the East of England, which is prone to rain constantly and also that the house has been on the market for two years and probably will be for a lot longer. Thanks for the answers so far, most of them are great!
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