Maybe your tenant doesn't want to sign, but is non confrontational and therefore avoiding you. 

If he confronts you about moving forward with another agent, be polite and be honest.

It's not confrontational yet gets the point across.

Putting things in writing avoids personal confrontation.   

I really don't mean to be so confrontational but the ignorance needs to be addressed. 

I believe it also forces people who make erroneous statements and claims about an area back them up when confronted by those sincerely in the know.

So I confronted her, and she gave me some sob story about losing her phone.

What made it even worse in terms of the stress level was their confrontational, hostile attitude, constant lies and half-truths, which made it almost impossible to deal with them in a reasonable, business-like manner.

This business is full of surprises and instead of playing the blame game confront the problem and correct it.

If the tenant is right - confront the seller.