Sell with posts or DM? This is a very interesting topic that was I was asked by several models.
Selling on posts is a gamble, it is always good to have posts to sell on your wall, but you never know if or when people are going to buy.
DM's are different because the interaction could be right then online. You can control if you sell something on the spot, calibrate the price and find out the need for specific content for fans.
Besides this you can find out what kind of content people are generally looking for and do that type of content, this helps you for future sales.
This is why I recommend staying at least 8 hours per day on DM's so you have a solid interaction with your fans and sell on the spot also, I also recommend having some separate posts to leave overnight.
What is your experience with selling posts vs DM's?