How do you diligence the strength of a brand?

Hi guys:

I've been looking at a specialty apparel company whose brand has fallen out of favor for the past few months. I'm curious on how you guys would go about diligencing the strength of the brand and turnaround potential please? What I've done so far is 1) read through this company's past 20 years of history to see similar situations and how that had worked out, 2) read through a few similarly positioned brands histories and see how missing-trends have worked out for them, 3) industry brand ranking data. 4) google trend of the brand.

Aside from running consumer survey (which can be limited even with large sample), how else would you assess a brand's strength and if it can bounce back after missing a year's trend?

Thanks!