personnel have been trained to use the product of the allegedly dominant undertaking or where due to network effects the value of rivals’ products are lower because they do not have a large installed base of customers. For instance the value of a piece of software may not only depend on the intrinsic qualities of the product but also on how many people use it and thus with whom the new buyers can exchange files. Finally, the incumbent firms may through the use of long-term contracts with customers have made it difficult for rivals at a particular point in time to find a sufficient number of customers able to switch supplier that expansion or entry would be profitable.
4.2.3 MARKET POSITION OF BUYERS
Market position of buyers indicates strength of constraint they exercise 41. The market position of buyers provides an indication of the extent to which they are likely to constrain the allegedly dominant undertaking. However, given the fact that dominance is assessed in relation to a market, it is not sufficient that certain strong buyers may be able to
extract more favourable conditions from the allegedly dominant undertaking than their weaker competitors. The presence of strong buyers can only serve to counter a finding of dominance if it is likely that in response to prices being increased above the competitive level, the buyers in question will pave the way for effective new entry or lead existing suppliers in the market to significantly expand their output so as to defeat the price increase.38 In other words, the strong buyers should not only protect themselves, but effectively protect the market.
Possibility of separate markets for weak and strong buyers 42. On the other hand, if one or more strong buyers are able to extract more favourable conditions from the allegedly dominant undertaking than their weaker competitors, it may be appropriate to define separate relevant markets for, respectively, strong and weak buyers.39
4.3 COLLECTIVE DOMINANCE
See in this respect Case T-228/97, Irish Sugar plc v Commission  ECR II-2969, paragraph 101. Commission Notice on the definition of the relevant market cited in footnote 11, paragraph 43.