Stephen Klein, a biz dev guy from Instacart, emailed me to ask why I hadn't tried it yet. Here's my response:
Hi Stephen, I was excited to learn about Instacart offering deliveries from Costco. Unfortunately, your current pricing model makes deciding whether to use Instacart too expensive. It's not that your prices are too high. It's that I don't know if your prices are too high; that is, the cost of information is too high.
When deciding whether to use Instacart, my decision is between going to Costco or having Instacart go to Costco for me. In most cases, I would prefer to have Instacart go for me. (Sometimes, I might want to browse.) But to make the decision, I need to know how much it would cost me to use Instacart.
The current pricing model is not transparent enough to determine this cost. Your prices are not the same prices as those offered as Costco, so I don't know what the total cost of using Instacart is, and rather than spend the time trying to figure it out, I simply don't use Instacart.
My recommendation would be to change your pricing model to make explicit the cost of using Instacart. You could charge a fixed percentage above the Costco price, charge a higher delivery fee, or charge a per-item delivery fee, for example; whatever model would be both transparent and profitable.
The state is that great fiction by which everyone tries to live at the expense of everyone else. - Frederic Bastiat