Is free trial enough to judge proxy service?

As a rule, I try to test any product before buying it. And proxies are no exception, since their performance can be much worse than expected. So what checks would you perform on a free trial before purchasing a proxy service?

A free trial doesn't guarantee 100% that everything will work perfectly later, but it can reveal obvious problems right away. For example, if the speed is poor or ips come form a different operators than expected, you can usually identify that during testing.

IP quality for your specific use case, plus real speed and reliability at different times of day.