We have been sharing the benefits of packing in used boxes for many years and this photo demonstrates one of the advantages perfectly - more boxes for your money!
On the left is a pallet of used boxes, on the right a pallet of brand new boxes of a similar size, quality and capacity. The cost of each pallet is the same but there are 450 used boxes for the price of 295 new boxes so in this instance 52% more boxes!
As well as the obvious financial benefits there are environmental benefits too; every time a box is reused the demand for new boxes is reduced and consequently fewer trees are cut down to make to make new boxes.
Finally, packing your products in used boxes could reduce your liabilities under The Producer Responsibility Obligations (Packaging Waste) Regulations 2007, which states that packaging that has been used before does not need to be included in your packaging data. Source: gov.uk.
There are many benefits to buying second hand boxes, so if it's not absolutely critical that your boxes are brand new, consider the alternative.