Rule reminder
'Come' (how/as) followed by the indicative describes a real, factual manner. 'Come se' followed by the subjunctive describes an unreal, imagined, or hypothetical manner. The tense after 'come se' is always subjunctive (imperfetto or trapassato). The tense after 'come' alone is indicative.
Si comporta ___ fosse il proprietario di questo posto, ma è solo un ospite.