First things first - please deactivate the unit in your account! We certainly don't want other customers to reserve it.
Most facilities want to do right by the customer and accommodate them. If the customer reserved a 5X5 unit that you no longer have, contact the customer and see if they'll take a larger unit at a steeply discounted rate. Most customers understand that mistakes happen. As long as you're apologetic - but confident - on your call with the customer, you can normally save their business.
"Hi, this is (your name) and I'm calling from (storage facility name). We just received your online reservation for a 5X5, and I'm so sorry to say that I just ran out of those units. I didn't yet remove the unit from showing up online, but I'd still like to help you out. I have a 5X8 unit that I can rent you for just $5/month more than the 5X5, which is $20 off per month. That will give you some space to move around and access your belongings, even when they're in storage. Does that work for you?"
If you don't have any availability and you simply don't have any option to help the customer, we're happy to help. Just submit a ticket to our support team. Please let us know (1) The name of the customer, (2) Why you weren't able to accommodate them, and (3) If you've already spoken with the customer. We'll have our call center reach out to the customer and attempt to book them at a facility nearby.
NOTE: SpareFoot can't "delete" reservations. That means that even though you've asked us to rebook this customer, their reservation at your facility will still remain active in our system.