Thre is nothing illegal about placing an offer on a home without seeing it. Many times when I have difficulty scheduling a showing on a home, because of the owner, the tenant or even the other agent (yes there are difficult agents), we go ahead and place the offer "contingent upon viewing the home".
This way you get the Listing Agent's and/or owner's attention to respond.
I also have many invesors that know certain areas very well and just place offers on homes sight unseen because they don't care what the house looks like, especially if it is "cheap".
If you are working with an agent they will help you with the "little secrets" that can get your foot in the door on a property you may otherwise miss out on.
Let me know if you have any other questions.