NFTs (Non-Fungible Tokens) have seen significant growth since they first captured public attention in 2021. However, the NFT market is plagued by fake transactions and economic bubbles, e.g., NFT wash trading. Wash trading typically refers to a transaction involving the same person or two colluding individuals, and has become a major threat to the NFT ecosystem. Previous studies only detect NFT wash trading from the financial aspect, while the real-world wash trading cases are much more complicated (e.g., not aiming at inflating the market value). There is still a lack of multi-dimension analysis to better understand NFT wash trading. Therefore, we present the most comprehensive study of NFT wash trading, analyzing 8,717,031 transfer events and 3,830,141 sale events from 2,701,883 NFTs. We first optimize the dataset collected via the OpenSea API. Next, we identify three types of NFT wash trading and propose identification algorithms. Our experimental results reveal 824 transfer events and 5,330 sale events (accounting for a total of \$8,857,070.41) and 370 address pairs related to NFT wash trading behaviors, causing a minimum loss of \$3,965,247.13. Furthermore, we provide insights from six aspects, i.e., marketplace design, profitability, NFT project design, payment token, user behavior, and NFT ecosystem.

翻译：自2021年首次引起公众关注以来，非同质化代币（NFT）经历了显著增长。然而，NFT市场饱受虚假交易和经济泡沫的困扰，例如NFT洗售交易。洗售交易通常指涉及同一人或两个合谋个体的交易，已成为NFT生态系统的主要威胁。先前的研究仅从金融角度检测NFT洗售交易，而现实中的洗售交易案例要复杂得多（例如并非以抬高市场价值为目的）。目前仍缺乏多维度分析来更好地理解NFT洗售交易。因此，我们开展了迄今为止最全面的NFT洗售交易研究，分析了来自2,701,883个NFT的8,717,031笔转移事件和3,830,141笔销售事件。我们首先优化了通过OpenSea API收集的数据集。接着，我们识别出三种类型的NFT洗售交易并提出了相应的检测算法。实验结果显示：824笔转移事件和5,330笔销售事件（总计涉及8,857,070.41美元）以及370个地址对与NFT洗售交易行为相关，造成至少3,965,247.13美元的损失。此外，我们从六个维度提供了深入分析，即市场平台设计、盈利性、NFT项目设计、支付代币、用户行为以及NFT生态系统。