My neighbours are planning a single story extension at the back of their house.
A surveyor has been in touch (touting for business), stating that we should appoint a party wall surveyor for which the neighbours will pay.
Does anyone have experience of this, and is it a necessary expense?
I like my neighbours and don't want to needlessly ask them to spend extra cash on the work...but at the same time, we have a preexisting extension right up against where they'll be digging and I have nightmares about cracks and weak foundations as it is 
Thanks in advance, lovely hive mind!