Selling to the sellers
> expand into location-based mobile advertising
An advertisement is an advertisement. Most people have seen enough of them (or soon will have) to become totally immune to their powers. Either that, or the more impulsive and impressionable people who will forever be influenced by them will go broke.
Either way, the point of new advertising technology is not to sell more stuff to the consumer: we either ignore them, block them or would buy whether the ad. appeared on a mobile phone screen or on a billboard. No, the point of wizzy new technology is to convince those people who want to advertise their products to buy advertising space. That's the only real sale (as anyone who's watched Mad Men will surely have worked out) that ever takes place in the advertising world.
So add adverts to apps. Add location awareness, with local discounts, "today only" offers, e-vouchers, wowchers, "likes", groupons and all the other stuff. It makes no difference - I'll still ignore them. If I want something, I'll still search for the best price and most trustworthy vendor: not for whatever pops up on my screen as I walk past a coffee shop. If vendors want to spend their money, it would be better spent on improving the product and lowering the price.