In AdWords Campaign Settings is the option to set frequency capping. You can set an impression cap per user per day, week or month, and on the campaign, ad group or ad level. This is particularly useful under display remarketing campaigns because it allows you to limit the amount of impressions a visitor sees in a given time period.

Plus, AdWords allows you to set up a remarketing list, what they call an Audience, to target visitors for up to 540 days. A cool way to set up a campaign is to put the remarketing code that is set for 540 days on the site and then use the frequency capping option together. For example, put a frequency cap of 5 impressions per user per month per campaign. This way the same person will only see the same ad 5 times in a month. Then at the beginning of the next month they get another 5 impressions. If you updated your ad creative on a regular basis you could message that person every month for over a year by giving them one piece of information at a time about the features and benefits of the product you’re selling – instead of hitting them with the same ad over and over for 10 days and then giving up on them.
Couple this with a custom combination made up of other audiences, and once that person purchases, they could then get dumped into the post purchase audience and be messaged to become a repeat customer. I think there is definitely potential for a constant pipeline of educating and converting and re-converting visitors through out the purchase funnel with this strategy.