It is perfectly fine to ask guests to remove their shoe's. It is your house and your rules
No.
ok
You should remove all the poo.
ok
It depends on what happens because the product is faulty. If you are selling a computer that is faulty because the space bar sticks sometime, then that would be OK. BUT, if you were selling a computer that will explode killing everyone in a 100 yard radius, then this is not OK. Is the product dangerous? If not, then it should be OK to sell, as long as you tell the buyer what is wrong with it and don't try to defraud your buyer.
ummm.. ok then
yes it is
"Advertise them in the paper." is OK for most states, but some states do not allow resale, so be sure to check with the state before putting ads or selling them, unless its a family member or a close Friend, those kind of people.
At home if nobody objects why not?
Absolutely
yes OK