Do'nt know if this is of any interest to anyone.
I have item's that are far to big for delivery companies.
Problem was that customer could still check out with postage price fixed at weight rate,
Solution. add a -10kg price to the zone rate at £5000.
List the weight of the item that is collect only as -10kg and hey presto, they will not check out with postage at £5000.00.