Hello,
Only Hikashop can decide if an order can have free shipping or not.
But generally it's related to the cart (weight+dimensions) more than the rest. If the cart need a shipping method and there is no method available the customer won't be able to finalize its order.
I think that you want to have some kind of "free" manual shipping method which would be only available when there is no method available.
That kind of feature would be possible thanks to a custom plugin, but it is not something related to HikaMarket or the vendors.
It is more a "fallback" to provide a solution to customer to finalize their orders even if there is no shipping method available.
But generally speaking ; it won't be something I would recommend since a customer would be able to pay and would expect its order even if he didn't pay for the shipping (which would add additional cost that he did not pay).
Having a feature which could tell the vendor if he has correctly configured its shipping method would be interesting but it would require to let each shipping plugin include some special code to "test" the configuration to see if it's working correctly.
Like that, I'm afraid that it would be very difficult to implement and push to the existing shipping plugins.
If you have other idea, feel free to share them ; maybe we can come to a interesting idea for implementation
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.