Note: this chapter explains how to use a more secure alternative to the traditional, centralized darknet markets. While it is optional to use this alternative (called OpenBazaar) you should take a look at this guide and follow it if you have the choice to buy from a vendor through OpenBazaar (e.g. because he links his OpenBazaar store link in his profile description of a traditional market).
OpenBazaar (short OB) is an open source project developing a protocol for e-commerce transactions in a fully decentralized marketplace. It uses bitcoin but also plans to support other cryptocurrencies in the future.
So basically it is a DNM as you know it but without anybody being able to shut it down since it is de-centralized (no single server that can get seized). Vendors are in control over their own stores and to take such a store down, LE would need to bust the vendor. Even then only one vendor would disappear with all the others still being able to vend as usual.
This is assuming that there is no grave bug / vulnerability in OB which makes it possible to disrupt the activity on OB or attack and possibly de-anonymize OB users in some way. To make sure the damage in such cases stays as small as possible it is extremely important that you not only set up OB properly but also follow the rest of the DNM bible. This is not the time for shortcuts. Your life and future is literally at stake. So take the extra mile and do it right.