In this purchase path the consumer does a search and on the same day makes a purchase. Then over a week later they receive a sales/customer service call. A few days after that they make another purchase.
a) In this attribution rule, you are choosing to allocate the credit for both sales to the original search ad. The argument for doing this is that without the original search ad, the salesperson would have no one to call. Therefore the ad that got the customer deserves all the credit.
b) In this attribution rule, you are giving conversion credit to the item that occurred prior to the sale- either the ad or the call. The argument for doing this is that you believe the sale should be allocated back to the most recent engagement with the consumer.
c) In this attribution rule, you believe the initial ad that got the consumer in the first place deserves some credit for future sales. The argument for this rule is that the ad that introduced the consumer to your business and lead to the first conversion deserves a percent of future sales that occur. Also, the addition of the sales call is worthy of some percent of the credit for future sales.