A no deposit bonus sounds like free money, and technically it is. Whether you ever get to keep any of it comes down to three numbers most players never read before they click claim.
The wagering multiplier is the real price tag
Every no deposit bonus carries a wagering requirement, usually written as a multiplier like 30x or 50x. That number tells you how many times you need to turn over the bonus amount in real bets before you can withdraw anything. A $10 no deposit bonus at 40x wagering means $400 in total bets before cashout, which on most pokies takes longer than it sounds once you factor in bet size limits. Smaller bonus amounts with lower multipliers are often more realistic to clear than a bigger headline number wrapped in a steep requirement.

Max bet and max cashout caps
While wagering a no deposit bonus, most operators cap the size of each bet you can place, often around $5. Bet above that limit and the whole bonus can be voided, not just the excess. There's usually also a max cashout on winnings from the bonus itself, commonly somewhere between $50 and $100 regardless of how much you actually won playing it off. That cap is the real ceiling on what a no deposit offer is worth, and it's worth checking before you get attached to a lucky run.
Where the good ones actually sit
SpinFin and X3Bet both run no deposit promotions from time to time with wagering and cashout limits stated clearly on the promo page rather than buried in a general terms document. That's the detail worth checking before you claim anywhere: if the cap and multiplier aren't visible on the offer itself, read the full terms before you spin a single credit.
Before you claim a no deposit bonus, find the wagering multiplier and the max cashout cap first. If either number is hidden behind a generic terms link, that's worth five minutes before you play, not after you win.