It's very variable though.Gumtree which belongs to ebay, I have sold loads of stuff including cars and found it very good. I would find the new price of your Machines then roughly half it for a second hand sale.
If it's some old / tired / no name tool you might be lucky to get 20% of new price.
If it's premium Festool / Fein / Mafell in little used condition you might get 70%.
Being willing to box something up and post it gives you a nationwide audience. Selling collect only means a lot of potential buyers won't travel or if they will, they'll have to factor in the cost of time, fuel and maybe even van hire. That quickly exceeds the £70-100 cost of sending a machine on a pallet.