Businesses often ask users to print a web page or a PDF file, sign it and return it by fax.  But no business I know of check whether the signed document has been changed from the original or not.  Even more troublesome, signatures are almost never verified.  In most cases, there is nothing to verify against.  All the contracts I have signed and faxed could have easily been signed by my son yet no one would know.  Is it the high legal cost that prevents disputes?  It seems to me that there is a market here somewhere.