It largely depends on the make and age.
For professional 3 phase equipment there seems to be 2 tier pricing, from a dealer, checked, tested and with a warranty will be worth much more than the same machine sold as seen from a private ebay sale.
Big brand names like Wadkin, Sedgwick, SCM, Axminster will have better sale value than lesser known brands.
If you want to name the machines it may easier to advise a source for pricing