I recently booked some trips through Viator, an aggregator of travel tours worldwide. For some reason, only known to Viator themselves, once you select the number of travellers for one tour, you must use the same number of travellers for all other tours added to the same order. If you wish to book one tour for 2 people, and another tour for just 1 of the people, you have to place them as separate orders.
Here's a screen capture of the way the tour page looks before selecting the number of travelers.
Here's a screen capture of the way the tour page looks after you have added a tour to the shopping cart with a set number of travelers.
You can't change the number of travelers anymore. Now, Viator does do a good job of providing a link with an explanation.
A business process that makes sense internally to a retailer doesn't necessarily make sense to shoppers. And sometimes business processes can get in the way of sales. If I have a one-time use promotion code, but want to book tours for different numbers of travelers, then I can only use it once and the rest would be booked without the benefit of the discount.
Frustrated Shopper Suggestion - Retailers need to look at their business processes from a shopper perspective and try to change it to be as convenient and understandable as possible to maximize conversion.
That's all for now. Gotta go shopping!