Are countdown timers considered pushy?

As an e-commerce business owner, I'm concerned about using countdown timers in my promotional strategy. While they seem like an effective way to create urgency, I worry they might come across as manipulative or aggressive to potential customers. I want to understand the psychological impact of these timers, whether they genuinely improve conversion rates, and how to implement them in a way that feels authentic and customer-friendly rather than pushy or deceptive.