Most of what you buy happens on other accounts, so what you can verify on your own side is thin.
The quality of trial services may differ from paid ones — the free trial is there to show you how it works.
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The activity happens away from your profile, on accounts you do not control. Your side of it is thin by design, which means the usual method of writing down a number and comparing it later does not fully apply. Decide in advance what you will accept as evidence: usually the order status plus whatever notification your own account receives.
Confirming the route works on your account and getting a feel for what twenty of these actually look like in practice. That second part matters more here than with most metrics, because expectations about this service tend to be much larger than the reality, and seeing the small version corrects that early.
What it will not show you is whether any of it produces attention worth having. That depends on where the activity lands and on what people find when they follow it back, neither of which a demonstration can arrange.
Short answers to what people ask most before ordering.