I thought this may be of use as I have just done so, having posted sun canopies in the past.

Sellers may not be aware how easy and reasonably priced this is to do.
For smaller items I use Hermes, but for heavier goods I use parcel2go. They are a sort of comparison website and give options for the seller to drop off at a local shop or have collected. You can adjust the insurance provided and choose length of delivery time. Some couriers even offer a collect service and print the labels for you.

Two 14kg parcels, poles and awning fabric, to Scotland from Essex took 3 days. £30 insured for £200, printed my own labels and droped off at the Post Office for Parcel Force to collect. I wrapped some card around the ends of the pole bag and wrapped it in a thick black plastic bag. The awning bag was also wrapped in a thick plastic bag.

So if you are trying to sell, it's worth considering.

Colin