A "guest friendly" hotel is a hotel which allows unregistered guests (commonly prostitutes) back to the room. This is a popular "feature" in party towns or in towns where foreigners come to "meet" locals.
Many hotels do not allow unregistered guests to spend the night -- even when accompanied by a registered guest. In some countries, hotels will charge a "joiner fee" for any unregistered guests.
"Guest friendly" hotels are also sometimes called "no joiner hotels".
Russian girls are awesome. Make sure you stay in a guest friendly hotel.