Any of the ideas can be funded and you need to figure out what would make it stand out from the crowd and what value your product would bring to your users (you know the story how Google was funded - the VCs simply liked the product).

1. Tons of competitors. I read a report somewhere that people use a weight-loss app for less than 2 weeks on average and then switch to another (I guess they don't like results). Thus, you will need to figure out retention problem (e.g. many such apps now include a hardware component).

2. There are tons of "deals" website (in the US) and many have forum format, up/down voting, etc. Key problem to address is how to get enough people to use the product and how to build critical mass.

3. The online sellers marketing automation exploits the fact that you can click on the link and buy the product. With offline stores you need to either force people to go to the store right now (hard) or to remember this marketing email long enough (days if not weeks) until they get into the store (also hard). Can you use location for that? Bluetooth? WiFi? Or is there something else that can help you to get people to buy things after they read your emails?