There are two questions that need to be answered here:
1) “Will it increase the sales?”
Maybe. Depends on how well you use it. What conditions need to be in place for your social media advertising to make an impact on sales? (that’s in this post!)
2) “Will you be able to attribute the sales increase directly to social media?”
Usually no, unless you designed the marketing message exactly for the traceability purpose. (More on that here) Let’s start with the conditions. Just like with traditional advertising, you have to generate enough impressions, with the right audience, using the relevant, effective message.
Right impressions for the right audience.
If you have a sizeable follower base, some of those impressions will be free of charge (anywhere between 5-10% of your followers will see your posts organically). All social media advertisers will need to pay to boost the number of impressions beyond their organic reach. Now, let’s select the target audience. You want the people that are most likely to show up at your restaurant. What does this mean for targeting? Geography: usually a 2 mile radius for suburban, 0.5 mile radius for dense urban. Down to less targets than you expected? Not the worst thing in the world… because now you may be able to afford more impressions per target! Demographics: age (exclude anyone too young or too old to be interested), gender (if relevant to your business model), primary language, etc. Targeting by ethnicity or race can make business sense, but it’s also getting into a legally and morally tricky territory – a separate blog post is in order. Psychographics (oh, it’s so much easier with the social media tools!): find the people that are interested in similar restaurants to yours, or people on the right life stage (i.e. families with young children, nearby college students, working professionals, etc), or people with interests that are relevant to your business (artisanal bakery? Find the fans of @mybakingaddiction; brewery and pub? Fans of @craftbeer.com are your friends). Next, what’s your expectation about your ad performance? How memorable is it? If 100 people saw your ad once each, how many of them would remember the offer, book/order online or remember to ask for the offer during the in-store visit? What if those 100 people saw the same ad 10 times each? 1000 times each? You know that once is probably not enough; 1000 times is probably an overkill. A very strong message (“Free steak dinner!”) needs lees repetitions than a weak one (“Free soda with a burger/fries combo purchase”). Practically, 10-50 impressions per person over a short period of time (less than a week) should give enough exposure to deliver results. The strength of the message and the quality of execution of the message will determine how many times you need to display the message to each user. Presuming that the message is effective, if all of the conditions above are met, your social media marketing is going to increase your sales.