Taxing land:

* violates no human rights (unlike taxes on income and sales)

* costs very little to assess and enforce (unlike taxes on income and sales)

* is impossible to evade (unlike taxes on income and sales)

* causes no economic harm in disincentivizing productive activity

* enables the funding of public goods (in this respect, it is similar to all other forms of taxation), and

* increases economic efficiency by discouraging wasteful use of land.

In Adam Smith's time, the biggest rentier of them all was the Imperial era British government along with its patrons, titled members of the nobility and the landed gentry. Even in Smith's time, free markets did mean freedom from government interference.

Out of curiosity, where specifically do you find this definition within Smith's writings?

Here's some

https://www.goodreads.com/quotes/6536394-as-soon-as-the-land...

https://www.adamsmithworks.org/documents/chapter-xi-of-the-r...

I was hoping OP would respond.

I'm familiar with both passages.

Neither contain a definition of "free market".

(That's a term Smith uses exceedingly rarely. Only once AFAIR.)