John,
B153 Urine Neutraliser is an excellent product, but do not promise too much.
Remember that the contamination may not be limited to the carpet - penetration to the underlay and beyond is common. Underlay contamination often covers and area twice as large as the visible stain and may be as large in any wooden flooring.
If it is a small puppy then surface treatment may suffice. Apply enough B153 to penetrate as deep as the urine and allow good dwell time. Be prepared to treat also for cellulostic browning and advise the customer that the staining may be permanent, especially where subjected to high levels of UV light.
Ventilate the rooms well to remove contaminated air and a post-treatment with a bactericidal odour neutraliser will also help.
This treatment may not be totally successful and a further visit, possibly to renew the underlay, treat the back of the carpet and possibly even the floor beneath may be required. The customer should be made aware of this before you start.
John.