If it's particularly heavy or oversized then try www.shiply.com where couriers bid for the job. If the seller is unwilling to wrap/pack the item then you can specify it in the job description... If you arrange for someone like ParcelForce to collect and when they there it's not suitably prepared for transit then they could decline to take the item.
Hope you manage to get it sorted it often amazes me on ebay where an item has gone for a stupidly low price as the seller states 'collection only' because they can't be bothered to price up couriers...it's not that hard!
S.