How does OPM collect prices?
Primary source
Verbatim text below is from the Electronic Code of Federal Regulations (eCFR), a public-domain U.S. government work. Always verify the current version with the eCFR before relying on it for any legal matter.
Full Text
(a) OPM collects most prices by visiting or calling retail outlets in each survey area and observing or verbally obtaining the item prices.
(b) OPM prices some items by catalog, Internet, or a similar source. Other items, not normally sold within an area, may be priced in a different area. In either case, the price of such items includes any applicable taxes, shipping, and handling charges. When an item is normally sold within an area but is not available at the time of survey, OPM may, on a case-by-case basis, use the price of the item in a neighboring survey or COLA area.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.