From what I understand they don’t really keep their value. I would put a normal one into an online trade in platform, then put the Hermes. Calculate any % difference if there is any.
Then look on eBay for guide prices for a 5 (or Hermes if you find any) and make a guesstimate from there.
As im sure you know people who want hermes ‘typically’ want the brand and latest thing, their interest decreases dramatically as the series you’re selling gets older in generation.
The bands hold their value better, especially if they’re old and no longer available, some people have a ‘got to have the whole collection’ illness/interest
Edit: sorry, totally misread the question, you were asking about buying a S7 not selling a S5.
My last two words of the day where just ‘unhinged’, and ‘zany’… hmm how much data can these sensors pull from your body anyway….