What it is. Services promising to "thicken" your file fast by stacking several paid authorized-user tradelines or other "score hacks."
Why it's risky. It's the paid-tradeline problem multiplied — temporary, expensive, and a pattern both scoring companies and regulators watch for. Money spent here is usually gone with nothing durable to show for it.
What to do instead. Build steadily with your own one-good-account plan. There's no real shortcut that lasts. When in doubt, check with FundFoundr first.