Do timers work for returning customers?

I'm running an e-commerce store and have heard about using countdown timers for creating urgency, but I'm unsure if they're effective for returning customers. My concern is whether these tactics feel manipulative or if they actually drive conversions for customers who already know and trust my brand. I want to understand the psychological impact, best practices, and whether timers can genuinely motivate repeat buyers without damaging customer loyalty or perceived brand authenticity.