Product trial and repeat purchase
Product trial is a consumer’s opportunity to test a product or service, usually without charge.
Repeat purchase is purchasing a product for a second time (or more!).
Upsides and downsides;
Upsides; The customers may like the product and buy it.
Downsides; The customers may not like the product and never come back.
A famous example would be - Greggs, they sometimes stand outside the shop and allow you to try sausage rolls.