My best advice for other user groups would be to approach the manager of the retailer they want to develop a relationship with. Go in with an open mind, lower the defenses and try to explain how a good relationship can benefit both parties. Don't go in slinging arrows. Start a dialog. Understand their issues.
Retailers run businesses.
They need to make money. Understand their limitations and offer ways to help. Bring a value proposition. Retailers are busy, so do the work for them. Offer a plan of action that clearly benefits their business.