Scottish: no, not the man who keeps asking you for huge chunks of your hard-earned money.  This refers to a man who holds a tack from another, a tenant.  In Scottish law, a tack is a contract by which something is let, hired or leased to another.

‘Tacksman’s house.’

Source: Adam Nicolson, Sea Room: An Island Life (London: Harper Collins, 2013 (2002)), p. 253