Depending on the size of the unit, $4000 doesn't seem unreasonable, but I'm sure that you can get a less expensive one. 

Right,  I agree with others, tell them no or they will start being more unreasonable 

I believe based off comps in the area that I could still get more rents out of it without being unreasonable.

What I think is unreasonable is that they withheld the terms of the mortgage until after I had incurred costs.

My point is that by and large most requests are not unreasonable and will ultimately benefit you.

As @Wayne Brooks says, financing contingencies are common, however his terms for this in your case are not and are unreasonable for the reasons you point out.  

Not to mention that Joe probably doesn't know what forms and disclosures to use to keep him out of legal trouble, how to instigate a bidding war, how to best handle multiple offers, how to push back on unreasonable buyer demands, how to negotiate the best terms, how to run an open house, how to document and handle escrow funds, etc.A lot of people think agents just show a house, shake a few hands and collect big fat checks. 

if I'm a buyer's agent I will not allow my client pay so much for a house that is not worth the listing price because I will religiously pull comps and if your price is unreasonable?

Do you think that sounds unreasonable?

I don’t think that is an unreasonable question.