IMHO when renting out an apartment it is very reasonable to charge whatever the going rate is (although don't be the one being mafkia sheorim). The fact that rents were half the price a few years ago is irrelevant. On the other hand when raising an existing tenant an excessive amount even if that is current market rate or trying to evict a tenant because his rent is low, that is a different story. Otoh a tenant expecting not to be raised when rents have gone up 50-100% isn't reasonable either.