It spends but does not sell
If money goes out and orders do not come in, the usual culprits are wasted search terms (clicks, no sales — block them as negatives), bids set higher than the keyword converts at, or a listing that does not convert the clicks you are buying. Start with the search-term report. See the full breakdown in why your ads are losing money.
It barely spends at all
If your ads hardly show, your bid or budget is usually too low to win the auction, or your keywords are too narrow. Raise the bid in small steps and check your impressions — low impressions means a visibility problem, not a relevance one.
You change it too often
PPC needs data to judge. Flipping campaigns on and off or slashing bids every day never lets a keyword prove itself. Give changes a week or two, then act on a fair sample — not five clicks.
Fix it consistently
Most "PPC not working" cases are really "PPC not maintained." AIAdKing runs the fixes every night — negatives, bid trims, budget, dayparting — with a logged reason and a shadow-mode preview, so the account is always being worked, not just when you remember.