Fear is probably the most common emotional tool scammers use to lure victims, with greed a close second. But there are scams that use a different human trait entirely: the desire to help others.
In this type of bad check scheme, a stranger approaches a potential victim as they are either heading into a bank/credit union, or walking up to an ATM. The stranger will ask the mark for help, giving an emotional, convoluted story for why they need cash right away, but can't get it from their own financial institution.
The con artist will then ask the victim to cash a check and hand over the funds, either by taking it to a teller or making a deposit into the ATM and withdrawing the funds.
What happens next is not difficult to predict. The check will turn out to be fraudulent and the victim has lost every dollar they gave to the scammer. The financial institution will never reimburse the loss because the victim is the one who deposited the bad check.
As an additional bonus, the victim may have their account terminated, since most deposit accounts come with an agreement that the consumer will not use the account to transact business for anyone who is not an owner of the account, and using it as a check-cashing service could be considered a violation of such terms.
Never trust anyone approaching you as you enter a bank or at an ATM. Decline as politely as possible, lie if you have to, and don't let on that you're wise to the scheme. Just get away, get as good a description as you can without being obvious, and contact law enforcement. This isn't the kind of scam that the perpetrators try on a single person and then give up. They will be waiting for another victim.