This list is by no means exhaustive, but is a useful guide to
the pitfalls and problems that can arise with
promotions:
Cyclical
promotions - you should avoid cases where an item can appear
on both sides of promotions, as you can have situations where buying
one item earns you another for free, and having 'bought' that item
then earns you another item for free, and so on. Remember that items
can be included in promotions through being in a certain category, as
well as by being specifically
included.
Promotions
involving items with different prices - for example, let's
say you have a buy one get one free promotion on a
product that has four differently priced versions. If a user picks two
items, you would typically want to give the cheaper one free. However,
if they buy 4 items together, and you just give the 2 cheapest free,
it may cost them more than if they made two separate purchases of 2
items (where they could get the cheapest and second most expensive
items for free instead of the two cheapest). The logic of dealing with
such promotions in the fairest way possible is highly complex and
dependent on a number of factors; what seems fair in one situation may
well not seem fair in another. It is far simpler to have buy
one get one free type promotions only on items of the same
price.