Despite significant strides in training expansive transformer models, their deployment for niche tasks remains intricate. This paper delves into deception detection, assessing domain adaptation methodologies from a cross-domain lens using transformer Large Language Models (LLMs). We roll out a new corpus with roughly 100,000 honest and misleading statements in seven domains, designed to serve as a benchmark for multidomain deception detection. As a primary contribution, we present a novel parameter-efficient finetuning adapter, PreXIA, which was proposed and implemented as part of this work. The design is model-, domain- and task-agnostic, with broad applications that are not limited by the confines of deception or classification tasks. We comprehensively analyze and rigorously evaluate LLM tuning methods and our original design using the new benchmark, highlighting their strengths, pointing out weaknesses, and suggesting potential areas for improvement. The proposed adapter consistently outperforms all competition on the DIFrauD benchmark used in this study. To the best of our knowledge, it improves on the state-of-the-art in its class for the deception task. In addition, the evaluation process leads to unexpected findings that, at the very least, cast doubt on the conclusions made in some of the recently published research regarding reasoning ability’s unequivocal dominance over representations quality with respect to the relative contribution of each one to a model’s performance and predictions.