If I inherited property with a fair market value of 150,000 but sold it at it's tax value of 123500, would this be considered a loss?

[AlanT222]

Assuming you did not use the home as your personal residence, if you sell an inherited home for less than its stepped-up basis, you have a capital loss that can be deducted.  You can deduct your capital loss from any of your capital gains.  However, only $3,000 of such losses can be deducted against your ordinary income per year. Any excess must be carried over to future years to be deducted.

If you used the house as your personal residence, you will not be able to deduct any of the capital loss.  

[AmeliesUncle]

It is a loss, but whether or not that loss is deductible or not depends on the circumstances.

If it was valued at $150,000, why was it sold for much less than that?

[AmyC]

Publication 544 (2019), Sales and Other Dispositions of ... has the answers. Why it was sold, to whom, what you did with the money, can affect you.

For example, the house is often sold to a family member at a lower price. This is not a loss for you.