$25 is not an OK rate if its a targeted shop.
It might be considered OK if the guidelines say you can shop whoever answers the phone.
If its a targeted shop, and you can ask for the target, that helps. If you are lucky and the target answers on your first call attempt, but if not you could spend three or four days trying to reach target.
The reports are long, with many narratives, you must be detailed with your answers, or the editor will come back at you. They are time consuming and if broken down you will probably be making $5.00 or less per hour.
Asking for the target is not a dead give away that you are a Mystery Shopper. You can always say a friend was in an picked up one of your cards and recommended you, they might ask the friend name, you can always make up a name.
If someone other than the target answers they sometimes do not want to give out information on when the target will be available, or they will say they can help you.
Be prepared, say you would prefer speaking with them (target) and ask when would be the best time to reach them (target). If the call is recorded, do not give them your correct name and phone number because then the target will then call you. Thank them, get off the phone and try again the next day or whenever they said the target will be there. ALL this for $25.00..