Trial and free tier are not the same thing
Stamp Me advertises a 30-day free trial; Loopy Loyalty likewise. After that there is no free option — the meter starts at $49 and $25 respectively.
A free tier keeps working indefinitely at reduced limits. The distinction matters because a trial forces a buying decision on a schedule that has nothing to do with whether your program is working yet.
Test the mechanic before you pay for the software
The thing most likely to kill your program is not the software — it is staff not offering it at the counter, a goal nobody can reach, or a reward not worth the trips. None of those cost money to discover.
Run it on paper for two weeks if you have to. Count how many customers accept a card when offered. If that number is low, no platform will fix it.
When free stops being enough
Customer caps bite first. SMS Masivos' free tier stops at 30 customers, which a busy café passes in a week.
The second wall is usually locations or staff logins. If you need a second site or a second person scanning, almost every free tier ends there.