Website owners who create typosquatting websites should watch what they are doing. Two website owners have been fined by phonepayplus for their use of text messaging services which cost up to 1.50 a message. They got users to sign up by pretending to be the real website, replicating all the design and look/feel of the website. Examples of typosquatting would be wikapedia.com and twtter.com both have minor misspellings that are easy to accidently type into the address bar.
I don’t see anything wrong with the principle of buying a misspelt address for a popular website however It’s essential that you are completely transparent about anything you try to sell, and that you make it perfectly clear your website probably isn’t the one they were looking for (maybe even give them a way to reach the legitimate website, you are after all piggybacking on their success).