Can the strata manager give lot owners contact details out to a third party without the lot owners consent?
The SM can do this if a current owner approves it. It’s common practice when a prospective owner wants to do a thorough search and it’s just a way of speeding up the process that would otherwise involve the vendor getting the information then passing it on to their solicitor.
As far as the strata manager “taking instructions” from a purchaser’s solicitor, all you can do is to ask them why and if they refuse to answer, report them to Fair Trading or threaten to do so.