Quote from @Anthony Silva:
I have a second home that I use as a STR in the Outer Banks, NC. Can I buy another second home in the Outer Banks, NC for 10% down to use as a STR? Or would I have to buy it as an investment property with 20-25% down?
As a mortgage broker I can tell you this is underwriter discretion. Some underwriters may not care or ask, while others may scrutinize the situation. That's why you're getting different answers/experiences in this post.
Fannie Mae's definition for second home properties includes "must be occupied by the borrower for some portion of the year". An underwriter more heavily scrutinizing the situation might think it's unlikely you'll be vacationing to 2 different homes in the same area each year.
Generally speaking, I have not seen underwriters look too deep into occupancy concerns related to second home vs investment property since Fannie/Freddie installed new LLPAs a couple years ago that make the pricing for each aligned in most cases. There is now essentially no benefit to obtaining a second home loan over an investment property loan, except for the ability to do 10% down rather than 15% (minimum for investment properties).
This info is all related to Conventional mortgage financing. If you work with a local community bank or credit union or some lender that doesn't sell to Fannie/Freddie in the secondary market, their guidelines and pricing could be different on this matter.