Why Listed Prices Differ Between Sellers

A first look at a comparison table can be confusing: one listing for a compound shows a pack price two or three times higher than another. The spread can reflect differences in what is being listed rather than the price level itself. This note sets out the main factors and how this index handles each of them. Numbers used below are illustrative, for arithmetic demonstration only, and do not describe any real product or seller.

Pack size

Sellers offer different quantities, such as a 2 mg, 5 mg or 10 mg vial, or bottles with different capsule counts. Pack prices differ with quantity, so comparing pack prices directly mixes up quantity and price. The index records the listed price of the whole pack together with its stated content and divides one by the other to give a price per milligram. As an arithmetic illustration, 30.00 USD for 5 mg and 45.00 USD for 10 mg give 6.00 and 4.50 USD per mg: the higher pack price is the lower figure per milligram. Each pack size on a seller page is recorded as its own listing.

Form

A compound may be listed as a vial, capsules, a liquid, a powder or another form. Products in different forms are not interchangeable listings. The index therefore calculates its summary figures, such as the minimum listed price and the median, separately for each combination of compound and form. A capsule listing is compared with other capsule listings, not with vials.

Shipping and order terms

The price per milligram is calculated from the listed pack price alone. Shipping charges, payment fees, minimum order values and voucher codes are not part of the figure. Seller profiles on this index can show whether a seller states free shipping or international shipping, but those details are shown as information next to the price, not folded into it. Two listings with similar per-mg figures can therefore end up costing different amounts once such terms apply.

Sale prices and timing

The index records the price as displayed when the listing was last checked. If a seller shows a reduced price at that moment, the reduced price is what appears, and a later return to the regular price appears only after the next update. Each listing carries the time it was last updated, and listings that have not been updated within the configured period (30 days by default) are marked as stale. Comparing a recently updated listing with an older one can show a difference that reflects timing rather than a current gap.

Currency and exchange rates

Some sellers list prices in a currency other than US dollars, such as pounds sterling. The index keeps the original price and currency and converts to USD using a stored exchange rate set at import time (manually maintained). The rate used is saved with each listing, and a later change to the stored rate applies only to listings imported afterwards. As an arithmetic illustration, 20.00 GBP converted at 1.30 USD per GBP becomes 26.00 USD; at 1.25 it would become 25.00 USD. Part of the difference between a USD listing and a converted listing can come from the rate rather than from the seller's own pricing.

Stock status

Listings marked out of stock are still shown, labelled as such and placed at the end of their group, but they are left out of the minimum listed price, the median and the seller count. A low price on an out-of-stock listing does not affect these summary figures until the listing is back in stock.

Reading the spread

Where listings for one compound span many pack sizes, forms and currencies, a wide range of listed prices can result. The per-mg figure, grouping by form, the last-updated time and the stock label are there to make that range readable. None of these figures is a statement about the content or quality of any product, and a lower figure is not a ranking of sellers.