We examined whether mimicking an interaction partner is universally advantageous or, provided the mimicry is particularly strong, whether it has detrimental impacts on interpersonal and negotiation outcomes. Participants interacted with a confederate who engaged in no, subtle, or strong mimicry and then negotiated. In laboratory Experiment 1 (N = 71) and Experiment 2 (N = 149), subtly (vs. not) mimicked participants liked the confederate more, while strongly (vs. subtly) mimicked participants liked and trusted less. In Experiment 2, strongly (vs. subtly) mimicked participants were less susceptible to the first-offer anchor. The online Experiment 3 (N = 180) corroborated the too-much-mimicry effect: When participants became aware of mimicry, it exerted detrimental effects on liking and trust irrespective of the experimental condition. Experiment 1 and Experiment 3 found no too-much-mimicry effect on anchoring susceptibility. These findings show that (a) sufficiently subtle mimicry positively influences interpersonal outcomes and (b) too much mimicry backfires.