You look for comparable sales for other distressed properties that are similar and nearby and also counter that with finished version comps so you can see what your perceived spread could be.

In terms of maximizing your returns you want to compare the interest to an alternative.

They bought it and held it, come hell or high water.

there are ways to get around the highest and you also need to take into account the savings you will generally have on the purchase side when compared to other regions. 

Properties are sitting on market for a bit longer now that supply is slowly creeping back up. 50 days isn't too terrible compared to the greater PHX area. 

What happens to the 'comparable value' if the area is uninhabitable or a community that won't return for years? 

Maybe the P trap under the sink is not filling with water correctly and allowing sewer gas to come back in.  

There are plenty of deals in Philly on and off-market from wholesalers, who are pretty decent in Philly compared to other places.You will need to get your GC license here and learn the permitting process and necessity here as well.

The cost to maintain them probably wouldn’t be exactly 8x as compared to the single 8-unit, but it sure as hell isn’t a 1-to-1 ratio either. 

Roads, water/sewer, city services, heck even just the planning for such is not a simplistic thing for all.