This is Dallas from the Shopify Social Care Team.
For this particular case, I can't say for sure if they're going to be a partner on our app store or not. The best first step would be to reach out to Spiff directly to increase dialogue to see if this is a legitimate situation or not. After talking with them the steps that you take after will really need to be based on your gut feeling.
Whenever it comes to something like this I strongly suggest that you take caution and default to or gut feeling. It's always good to be extra cautious and it's never wrong to ask questions about something like this.
I know this might not be that answer you were hoping for, but those will be your best steps to handle this situation.