YouTube subscribers attach to your profile permanently, which makes them the one purchase on this list where retention is the whole question. Anyone can deliver a number for a day. What matters is what is still there in a month, and the honest position is that this is measured by almost nobody — including, at the moment, us. Ask a seller directly what their refill window is, whether it is automatic or a support ticket, and what happens if the drop lands on day thirty-one.
YouTube is the platform where buying carries a specific, named consequence, because it is the one with a monetisation programme attached to the numbers. The Partner Programme thresholds — 1,000 subscribers and 4,000 public watch hours, or 10 million Shorts views — are checked by a review process that looks at the shape of the growth, not only its total. Subscribers that arrive faster than the views that would have produced them, or watch hours against videos with no retention curve, are the pattern that review is designed to catch. It is also the platform where the numbers are hardest to fake convincingly, because watch time is a duration rather than a click.
Beyond the metric itself, the same four things separate a working order from a wasted one, and none of them are visible from a landing page. First: whether the seller asks for your password. No legitimate provider in this category needs one — a public username or a profile link is all the work requires — and a request for a login is the end of the conversation, not something to weigh against a lower price.
Second: whether the price you are quoted is the price you pay. Retail sellers here quote packages and panels quote a rate per 1,000, and the gap between them once you normalise is routinely fiftyfold. Every figure on this page has been converted to the same per-1,000 unit for exactly that reason.
Third: what the refill promise actually says. "Refill guarantee" is a marketing phrase until you read the window, the trigger and the process. Thirty days, automatic, no receipt required is a real guarantee. Thirty days, on request, subject to review is a support ticket you will probably not bother to file. Fourth: whether the seller has been trading long enough to still exist when you need the fourth one. Domain age is on every provider's page here, and it is the cheapest signal in the category.