The aim of this study is to investigate the pragmatic language behavior of Turkish learners of English in formal complaint situations through the comparison of their speech act performances to those of native speakers. The data was collected from a total of 276 participants, 132 Native Speakers (NSs) and 144 Turkish Learners (TLs) of English. Three different data collection methods were used: a) Discourse Evaluation Task (DET); b) video-recorded role plays; and c) open-ended oral interviews. The results indicate that native English speakers' and Turkish learners' production of complaints reflects a significant difference with respect to the linguistic components and the pragmatic choices made in complaining. A significant contribution of the current study to the literature is the Discourse Evaluation Task (DET), which is both a data collection tool and a term used for the first time in this paper.