Image via WikipediaRecently I received a promotion letter (20 EUR off) by Deutsche Bahn, the state-owned German train operator. In the fineprint it stated that it could only applied when booking through a sales office (instead of online), was good till September, had minimum requirements on the ticket price and the type of train, and most importantly, once applied was non-refundable. Because I wouldn't use it for private travel, I thought about saving some bucks for IBM and planned to use it for a train-based business travel for which I needed to apply the IBM corporate client tariff. And I had so-called BahnCard, a frequent traveler card for 50% discount. Looking back, combining all this, it already called for disaster.
Once I was next in line, I mentioned the corporate client tariff, showed my identification for the corporate client tariff, the BahnCard, and the promotion letter. Few minutes later, I had my ticket, the promotion was applied and the credit card was swiped. Unfortunately, when I held the ticket in my hands, I couldn't see the corporate client tariff. No problem, the sales agent said, we'll look into it. After consulting with another sales agent, the "application support" was called in on how to apply the corporate client tariff. Next, the old ticket was canceled and a new one generated, all looking good. The idea was to apply the refund for the old to the new ticket, putting the difference back to the corporate credit card. However, because of the non-refundable promotion, the system went into a loop. It could not fully cancel the old ticket because parts of it were paid for by a non-refundable payment. The sales agent went into different menu options for payment, trying to charge a negative amount to the credit card, trying to refund the difference as cash, etc. All actions produced error messages because of incompatible offer conditions.
After several long minutes and an increasingly long line behind my (now sweaty back), the sales agent decided to call in help from the application support center again. The support engineer was able to remotely log into the transaction and see details, but was neither able to cancel the transaction nor to complete it. Together, they discussed options on how to convince the system to "get the job done". Finally, with my OK my credit card was charged again - paying the ticket a second time. Then a cash refund outside the system was initiated after performing and documenting a full cash inventory. Eventually, I left the sales office after about one hour, smiling to the "next in line" call.
When you design promotions, make sure the system is not only able to handle them, but also all the error cases. Those are best practices of engineering.
