Free samples are a great way to create interest for products your current customers are unfamiliar with. It could even be a different variant. A new flavor, different color, different material, etc.
One thing I rarely see stores doing is to send unsolicited samples to customers. Instead of just talking about your new product, send the top 10% of your customers a sample of it. Add in some short copy about how valuable of a customer they are and you have an instant repeat customer perk.
I've seen this done when companies are chasing down new customers (e.g. personalized pens in the mail). It's rare though to see this once a customer has started to order, even though keeping those customers is cheaper and more effective in the long-run.
You can use the segments in Repeat Customer Insights to figure out who to send samples to. Start with the most loyal segments (VIP, Loyal) and see how those customers perform over the next few months.