For example a lot of beginners will see a cap rate that is very high for their market and think thats a good thing while more experienced investors will consider it as a red flag or an indicator that the property is undesirable for some reason: could be it is in a bad location, is in poor condition, will have limited appreciation, etc. which might be counter-intuitive for someone solely focused on getting a certain cap rate.

-Like @Dan Mackin said, VA loans can be undesirable to sellers.

As far as crime rates goes, yes I understand the stats, but I also understand that there are many neighborhoods in Detroit that are gentrifying and its matter of finding the gems in the rough and firing the trigger..... pardon the punI  did this in Atlanta, I purchased in neighborhoods that were considered rough and undesirable at the time for around $35,000 today this SFH are worth $185,000 each and renting at on average $1400 pm. 

All of these allows you to get back your initial cost (or more if you prefer to structure it that way).Regarding delayed financing, I've found it to be still undesirable unconventional, but it works for a lot of works. 

If I spend 500,000 6-600,000 here in La county for example, I will get a undesirable neighborhood, crime, low income, gangs, uneducated neighborhood and a house that most likely was built in the 1930's and outdated.

He has put a NOD on all three because lendee was late in April, making their properties even more undesirable to potential buyers, hindering their sales and is now considering on lending more for the condo's rehab to get it on the market.  

He inherited a bit of a mess from the previous owner (bedbugs, undesirable tenants, and deferred maintenance), but we're getting things straightened out. 

But I guess I’m assuming a $10k mobile home parked somewhere nice is worth more than one parked somewhere undesirable.

While that price tag is appealing, the trade off is often a lot of tenancy issues (including the whole Section 8 hassle with housing authorities), huge rehab requirements because of long-deferred maintenance etc,  as well as lost equity because homes in these areas are unlikely to sell for any substantial amount no matter what condition they are in, simply due to the neighborhood - so any refurb equity is basically cancelled out by the undesirable location and the condition of surrounding properties, crime rate, etc.If you do decide to go the TK route, I have a lot more to say about the questions you should be asking of any provider you consider (and if you look at any of my past posts, I harp on this point quite a bit).

There is always a 'range' of rental prices and the more you can keep your property at the top of that range, the more likely you are to have tenants who don't want to risk losing their place by missing their rent or other undesirable behaviour.