I've tried to sell these lots for $1000 over the past year and been told due to their location/slope, they are undesirable/worthless.

Redwood City has parts that are undesirable.

Here in CA, the challenges to development from a regulatory perspective make development undesirable for business people who take risks in exchange for profit. 

I will hate for you to place your private funds into undesirable areas, confusing condos, rusty mobile homes or go with an unscrupulous "partner".   

So, at least in my market, sellers that offer seller financing only do so because the property has major issues keeping it from being financed in the first place, or they are can't get any other offers for whatever reason (undesirable area, etc).There's a lot of talk on BP claiming seller financing is a great way to get into investing. 

That is a good idea.What was the most undesirable part about the one's you looked at?

Do you buy a property based solely on numbers or does the location play a part ... even if the numbers are good.I found a duplex in an undesirable community that I never even thought about.

This is an undesirable heating option here in the Pacific Northwest and I’m looking for the most cost efficient way to provide an alternative.

One problem that took me YEARS to learn was that a fixed up building in a bad/undesirable area of town is just not worth very much. 

Could be subsidized financing by Invest Atlanta, a few ugly houses on the same block, undesirable historic features like a shared drive, drug deal next door ...