It is tricky because, from what I've seen, people's buying habits are so inconsistent. I've been on 2 domestic and 2 DUB flights in the last week, and not one purchase was made on any of the 4 flights. Not one single purchase. On the other hand, I've seen cabin crew selling food and drink to at least 10 people in the first 4-5 rows on a MAN flight 3 or 4 weeks ago, with the crew not being able to make their way any further back before they had to stop service.