It's his choice whether he uses an MM or not.
Reasons he doesn't use an MM can include:
- He doesn't want to pay for fees
- He Doesn't think he needs MM
- He wants more trust/vouches
- His pins might not be 100% working, in which case if one failed, it would be messy with an MM
Whether it is one of these reasons or not, you should have read his thread and agreed to his rules before you contact him.
Also, for your reference:
The link method is completely safe, they can't get your password even if you have already logged in or whatever.
The seller often uses link method because he doesn't want to get into a dispute about whether his pin did or didn't work when you complain that it has failed.