Google PRINCIPLES OF MOBILE SITE DESIGN: DELIGHT USERS AND DRIVE CONVERSIONS - Manual (Page 15)

7. IMPLEMENT FILTERS
TO IMPROVE SITE
SEARCH USABILITY
Participants relied on filters to narrow down search
results, and actually abandoned sites that couldn’t
reduce volume. However, you also need to ensure users
don’t filter themselves into a box - one car dealer site
allowed participants to specify configurations that
didn’t actually exist. Help users avoid problems by letting
them know how many results will be returned with
a particular filter applied.
Key Takeaway
Offer filters to help users get what they
need from search, but make sure users
can’t filter a search to return zero results.
Example from Macy’s Mobile Site.
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