People who use private postal centers know there is a premium to be paid for shorter lines and faster service -- but how much is too much?

As Raquel Rivas had done at least a half-dozen times before, she walked into the American Postal store on Babcock Road to mail a book.

"One day, I took a book and the gentleman charged me $4.90. The next day, I took the same book, same wrapping, same everything and he charged me $12.90," Rivas said.

Rivas was equally surprised to hear how the store employee responded when confronted about the price differential.

"I was just here yesterday, it was $4.90 and now you're telling me it's $12.90," Rivas said she told the employee. "'What's going on?' He said, 'Oh, I had too much coffee,'" Rivas said.

She ended up paying only $4.90 but according to her, it was only because she questioned it.

The KSAT Defenders took the same book to the same store to see if there was consistency in pricing.

A Defenders producer was quoted $4.94 to send the book one day, but several days later, the price was $11.35 for the same book.

The higher price does elevate the service to priority mail, so if cost is a primary concern, it should be stated up front.

A week later, the Defenders walked into the same store with the same book asking for the best rate. It was $11.85.

The Defenders questioned the employee, after which he decided to classify the book as a package, rather than a large envelope, allowing him to send it parcel post and knocking the price down to $4.23.

Store owner Levy Martinez said he has some new employees and has noticed some discrepancies. He also stated he would be going over procedures and pricing with his staff.

It is worth noting that two other private postal centers quoted less than $5 to mail the same book.