Him threatening to "undo" the sale or seek damages is just that, a threat.

Hi,I have a rental property in Golden, CO and recently had a tenant move in that is verbally harassing, making threats to sue me and to "make me pay," and demanding repairs and cosmetic upgrades that are not necessary.  

Don't bend to idle threats.

It's not that I was in physical threat or anything, but I was just worried that I've never been in a low-income area, and I feel that I'm not prepared for the task.

(The neighbor trying to mow would be a threat.... the vibration of the mower is a big problem for bees).  

With holding money owed to me is a very serious threat to my business and I do not take it lightly.I know most landlords prefer to live with bad tenants that pay late, I do not.

But don't make threats you don't intend to follow through with.  

At some point many will tire of the threat and real estate values should drop or remain very low.

@Brian Ploszay Ya, trying to not resort to threats because I don't know the situation, but 2 weeks is a long time with no communication.. 

For example when the current tenant renews in 6 years they know (especially if they are represented) that the path of least resistance for you is to renew them, the threat of vacancy - particularly for a local owner - is daunting and tenants know it.