Going after already-established businesses?

Does anyone go after businesses that are already successful or established? How about businesses that already seem to have someone/a company marketing for them? What do you do differently when contacting them compared to others?

One example of a business I want to work with is a fine-dining restaurant, arguably one of the best of its type in the city. Its critic reviews are positive, however I just realize now that its ratings are around 3 stars on review sites and there are many negative Urbanspoon reviews. I think these are mostly due to using Groupons (where I figured they probably want more customers or repeat customers).

The restaurant group's website was infected a few weeks ago (links leading to Viagra) and is just redirecting to the restaurant I mentioned above now. I think I could still mention it.

The individual restaurant websites are all very different and mediocre and they seem to be powered by some restaurant-marketing app, so it doesn't look like they have a third party marketer. Okay, after typing all of that, I realized I have a lot to offer to them :p. Website makeovers, possibly reputation management (appears to mostly be service issues though) and maybe some advertizing or utilizing Groupon customers. Any suggestions about that last part? They have a mailing list on the websites. How could I suggest utilizing Groupon clients (assuming they don't already) and creating a list with them without them "stealing" the idea? Sorry about all the rambling.