I think the deepest discounts we get are smelly units. You know, the ones with multiple pets, heavy smokers, garbage hoarders, etc. Best ones: all of the above!
When we find a stinker, it smells like money to us. Not only do we know we are getting a deeeep discount, but we know there won't be any competition, either!
When you find a foreclosure stinker, it is even better. Bankers can't seem to stand smelly units. It goes against their sense of "order", as well as their sense of "odor"! They just want to get rid of it ASAP, and since yours is probably their only offer, they'll probably take it.
Getting rid of foul odor really isn't that difficult. Just removing the source goes a long way. Bit of scrubbing, and paint will complete the job. Make sure to use a sealing primer, like Kilz or Zinzer. We use an oil based primer for real stinkers. Make sure to cover all sufaces, including subfloor. You may need new sub-floor in some areas. Sometimes if urine is left to accumulate it can completely rot it out.
The difference you can make with this clean and paint is astounding. You can force up the value by tens of thousands! This will give you instant equity in a building, and give you a real head start in your investing if done with your first few places. You can then start buying "sweet smelling" units if you want.
Of course, after your first few, the stinkers will start to smell much better. they smell...kinda like money!