Bit of an unusual question - has your friend been given the yacht to sell by someone who is not able to, or inherited it or something? Obviously none of my business but would have thought any owner of a 10m yacht would be aware of the different avenues for selling it. Anyway to answer constructively; I have refurbished and privately sold 13 yachts in the 6-9m range over the years, only one timber though.
Listing it on a site like this would be a good cost effective start;
www.boatsonline.com.au/private/sell-my-boat.html?utm_source=loopa&utm_medium=googleads&gad=1&gclid=EAIaIQobChMIqf3Q1KDH_wIVyaKWCh2EZwlzEAMYAyAAEgJhC_D_BwEBut be prepared to spend a lot of time and effort "entertaining" tyre kickers. In basic terms selling a boat privately is usually a nightmare.
If the yacht is in good condition with a good recent survey it will help significantly. What design type is it, who was the builder, how old is it, rig and standing rigging in good condition with the latter less than 10yrs old, diesel running, serviceable sails, all running rigging, anchor and warp etc etc.
Good prior post here of selling in general not a 10m timber yacht in WA. What part of WA?
www.seabreeze.com.au/forums/Sailing/General/Best-way-to-sell-a-boat?page=1There are numerous good checklists on line which the seller should have the answer to. eg
www.practical-sailor.com/sailboat-reviews/used_sailboats/diy-survey-checklist-for-used-boat-buyingAll the best with the task.