According to data from a Harvard Business School publication, only 16% of signed letters of intent to buy a company in the US result in closed deals. The remaining 84% of M&A deals flounder.Why? DYP Advisors, a firm specializing in corporate and intellectual property law, says four due diligence mistakes are to blame:1. Site sellers failing to do due diligence on the would-be buyer’s operations, cultural “fit” and finances.2. Sellers who haven’t prepped their internal accounting and legal records properly prior to a sale.3. Sellers who hide key information from would-be buyers.4. Sellers who reveal company secrets to buyers before checking with their lawyer about what’s OK to reveal.Having sold a membership site myself in 2007 and evaluated buying several others since, I can tell you that mistake number two (failure to prep internal records) is the biggest hurdle for small-mid-sized business owners. You’re so busy running your site that you never have time to clean up the paperwork mess. BTW: How much is your membership or subscription site really worth if you want to sell it to another publisher? Check out our sister site’s special report on site valuations here.