So for instance this would be fine:
- A web hosting company refusing clients, because you can use another one
- Amazon refusing to sell the item themselves, because other companies can sell on the Amazon marketplace
- A bank refusing a client, since you can just use another bank
This would not be fine:
- Apple refusing to list an app on the app store, since no else can do so
- Amazon refusing to allow an item on its marketplace at all, since there is no other way to sell to people who buy on Amazon
- Google banning something from their search engine, since that's the only way to reach people who search with only Google
- PayPal refusing a client, since using PayPal is the only way to easily accept payment from PayPal account holders