I pulled my house off of plugshare due to the majority of visitors not offering to pay for the power they were using. Apparently I was wrong in assuming that it meant share, as in share the plug and the expenses. I had one guy that started coming by twice every weekend to charge his Leaf. The last straw was when he started asking to stay overnight in our guest room.
Anyway, guests are welcome to charge. But if I were a guest I would at least offer to pay for the electricity I was using.