When I was there, quite often museums or cathedrals would not be open on the day I planned to visit them. Most places seem to have at least one day off a week and are usually shut on the last Thursday of every month.
Everywhere seems to offer a cheaper price for Russians than it does for foreigners, though there are ways to pay slightly less. Most places accept student cards and the OAP age is about 50, so if you are old or young you can get a discount.
I was lucky enough to go with Russian speakers, and we just pretended we were Russian usually!
Updates
Just to clarify, I was not implying that people who are over 50 are old. I meant that in Russia life expectancy is a lot lower than in the UK, which means their pension age is lower too.
Is this your business?