it depends on whether your friend has ticked the option to block
everyone except those in his contact list. say your friend does not
block everyone, if he appears offline but is actually online on the
block checker, then he has blocked you. but if he blocks everyone,
then he will appear offline in your list, as well as on the block
checker. you cannnot tell whether if you are blocked. thus, block
checkers only work 1 way
