One way i could see this evolving into, and I'd hope it would, would be in the way @actifit posts did. Adding a few curators to look for exceptional posts on any given day and adding some extra voting mana behind those posts, showing others that hey, if you add some more text, thoughts, originality, pics, effort into your physical activity counter of the app, people may value them more and also interact/engage and have more reasons to follow you, thus creating a healthy and genuine relationship between author and reader/also author as everyone on hive likes to post. This in turn brings a lot more value to hive than just posting a pic of a map with a line following a road you ran through and a number saying you got this many steps in, give me upvote.

This also prevents issues you mentioned such as multiaccounting, because people have gotta put in more effort into their posts, what were you doing that day, did anything happen at the market/on the way/after, you know, just blog, rather than just posting a proof of purchase and getting overrewarded for it. It kind of becomes vote-buy-ish as we also suffer from the effects of somewhat lately from some projects we've ignored for far too long.

So yeah, while the initial idea has value, as I said in my previous comment, if left stagnant it can quickly turn into abuse. So my suggestion would be, manual curators encouraging better content and that the app doesn't force people to instantly post the pics but let's them make a regular post about their shopping activity. With some potential more restrictions or whatever so it still far outweighs what other web2 projects/discounts can offer but not so much that it takes a big toll on stakeholders here while at the same time making many dislike what it is they're seeing.

I don't see a reason why the spendhbd activity can't just be an "add-on" to a regular post. Like, "oh and btw, we went shopping later that day and purchased this for a discount", along with an appropriate beneficiary forfeiture to the project that makes the discounts possible. Honestly, giving better discounts to "better" authors/social users doesn't sound like a bad business model either, maybe they'd try a bit more then! :D

Lastly, this is something for many "experimentative projects using the rewards pool" not just singling out spendHBD. For instance, while @redditposh may be giving out too much rewards currently to only ~50 weekly sharers give or take, it is based on attempting to encourage more people to join and hive prices being low. Naturally at some point this "early adopter" phase may start to diminish and people may not earn as much from the same sharing performance, especially if the price of hive remains the same and more people join in as voting mana is scarce.