I am sure the guy who spent $10k on a machine would prefer having it at his place more than having it sitting in your garage. Sadly I see only two choices - either "suck it up" and store it for him until you can get it to him or refund the money.

It isn't the buyers fault this Coronavirus mess has everything screwed up. It isn't your fault either. But all of us need to do what ever it takes during these crazy times to work together. Put yourself in his shoes and think about how you would feel if he wanted to charge you storage after you sent him $10k for a machine.