or some variation of that, I immediately tell them that I’ll call them back if I’m interested thank you and immediately hang up the phone to avoid wasting time.

While the areas with bad schools and perhaps some crime issues like the gentryfying neighborhoods in DC...Petworth, Brightwood, Ivy City, Brentwood....will have huge price variations based on the condition of the property.Now do flips happen in Fairfax and Montgomery County...sure, but in nowhere the same types of numbers that they happen in DC and PG County.It doesnt really speak to Dunkirk exactly, but I hope it sheds some light on how doing X, like rehabbing a bathroom could have a huge impact in location Y, but no impact in location Z, and thus why you can not really have a rule of thumb that spending A will return B. 

In these cases, even by adding a unit to the existing building, you are "Within COmpliance" of the Zoning Ordinance, and therefore there is no restriction.2) Variation: If the lot area is Close to what would be required (within 90%) you could qualify to pursue a Zoning Variation in order to permit the extra unit to be added.