My home's value has dropped is it because Coldwell Banker was showing it for sale when it wasn't?

Zillow's values are taken from tax records and recently sold homes in the area. Listing your house on zillow multiple times won't affect the actual value. Claim your own house and edit the information if you have made improvements. That should help the value.  

Zillow's Zestimate is not an accurate value.  It's hard for appraisers to even pinpoint an exact value, let alone an automated system.  In fact, the value of your home is generally what you as the seller and what a buyer would agree upon as the value during a transaction.

Unless you're looking to sell your home in the near future or are protesting a tax valuation amount, I recommend ignoring your home's value.  It can be a rough ride for a few years watching it go up and down, particularly if you are putting money into it.

If your tax valuation has increased, then you might be able to protest the valuation change.  Most markets have seen a decline, but many tax assessors are still increasing values to raise tax revenues.  You may not win, but putting more pressure on them will slow their bad valuation procedures.  We had a mess in our market with valuations in recent years.

Best of luck!