Using stable isotope mixing models (SIMMs) to quantify past diets is becoming increasingly common in archaeology. This study highlights important field-specific difficulties encountered by archaeologists in reconstructing palaeodiets using SIMMs. Focusing on the data acquisition stage, we discuss several issues that could confound dietary quantification if not accounted for. These issues are categorized under several broad categories: diagenesis, intra-individual variability, representativeness of both the consumers and sources, and other commonly encountered field-specific problems. We summarize these issues with a flow chart to help archaeologists to select the most appropriate samples for dietary reconstruction using SIMMs, thereby decreasing the probability that the outputs of the SIMM are inaccurate. We conclude by discussing the ways in which SIMMs may not be appropriate for all archaeological contexts, highlighting those areas that are likely to be the most problematic for end users.