Difference between 顾客, 客, 客户 and 客人 As in the title what is the difference in word usage/meaning between the following fours words: 


客 
顾客
客户
客人


?
客, guest, visitor. For a shop, it is customer.

顧客, customer. (顧, look back -> visit and revisit.)

客户, customer account, a customer with account. (户, the front door -> household -> account). Some ignore the concept of account.

客人, 人客. guest / visitor (of human).