One of my chief challenges is my tenants in a few of my properties.

Location

Difficult sellers (not allowing showings) 

HOA not allowing signs

1. Marketing to maintain strong buyer traffic
2. financing
3. buyers behind the pricing curve, and
4. sellers ahead of the pricing curve

1. Layout becuase we have odd shaped lots, small lot, and view corridors.  So to accomodate a view sometimes the house's layout is not preferable to all buyers.

2. Noise main roads and railroad noise

3. Condo HOA, some of our buildings along the coast are quite old and HOA fees are high due to maintenance/repairs

Tony and Suzanne - I think some things will be relatively consistent no matter the market. Other than price:

1. Location

2. Condition

3. Availability to show

4. Competition

Location

Sellers not being flexible with showings

Sellers not realizing the effects of all the new construction on home prices/appeal in our area

Some sellers do not allow a lockbox.

Some sellers do not let agents show homes on short notice.

Some sellers do not get the home ready for showings. 

marketabilty always comes down to three things

price

condition

location

price always solves the other two

Tony and Suzanne,
We have a few issues with location, soil issues, houses that face north, older styles (bi-level houses) but being a small market a house that is properly listed may have to wait a little bit until the right buyer comes along.

Competing with new construction, having buyers ask for all the closing costs and dealing with new agents that don't know how to write offers.

Dated or in need of repairs, doesn't qualify for conventional financing, new flood map puts it in a high flood insurance bracket.

Financing is the biggest challenge, educating the customer, other agents. 

Lenders, financing, appraisals, people believing the zillow/redfin estimates over their realtor.

Tony,

Again it depends, and I would agree with Sandy Padula and Norm Padula, JD, GRI ...A

Tony and Suzanne Marriott, Associate Brokers usually, price, terms and conditions are three main reasons for a home not to be sold.

The one I can add is - availability for showings.