With the
Shipping Director plugin, here are few possibilities:
1) Use the
ErrorExit rule [with expression, e.g., Items.Any(Product.Weight > 50) ] so that the customer cannot continue checkout. The message shown to the customer can explain details, e.g. remove item from cart to continue, contact us, etc.
2) Let the customer continue checkout, but warn them in the shipping method's Name or Description that they will be contacted with additional charges for shipment.
3) Conditionally call another shipping method/rate plugin to get the freight rates. (In the past, we've done custom plugins for ReTrans freight [now know as Kuehne+Nagel], YrcFreight, others.)
(FYI, rather Product.Weight > 50, you could use Product.HasCategory("...") )
Contact us at support at noptools.com if you need more information about Shipping Director.