Anyone can print a lanyard. If you want to be sure a card is a real StreetPay card before you pay, type the worker's name or the four character code from the back of their card.
This confirms that a card was issued by StreetPay and that the account behind it is active. It cannot tell you that the person standing in front of you is the person on the card. The photo on the card is there for that. Look at it.
If a card looks fake, or the photo does not match the person, call StreetPay on 061 628 2710.