Political micro-targeting describes the use of data to identify members of a target audience and send messages designed to fit their views and resonate with them. The practice has received considerable attention of late, especially around questions of transparency. This study explores one potential solution to this quandary, namely, disclosure labels. Adopting a pre-registered online one-factorial three-group between-subjects experimental design, we have investigated how different types of disclosure labels for micro-targeted advertisements impact source and message credibility, as well as source trustworthiness. Furthermore, we have investigated the potential mediating effect of persuasion knowledge on these effects. We exposed 227 German Facebook users to either a Facebook advertisement without a disclosure label, a sponsored disclosure label, or a targeting disclosure label that stated they were targeted based on their online behavior. The results demonstrate small and non-significant differences between groups regarding source and message credibility and source trustworthiness, with no mediation by persuasion knowledge observed. Additionally, most participants did not recall the disclosure we exposed them to, potentially explaining these small effects within our sample. In conclusion, our targeting disclosure approaches were insufficiently informative. Hence, we argue that platforms should put more effort into improving transparency for their users than they currently do.