Comparing completed sales with asking prices
An asking price shows what someone hopes to receive. A completed sale can provide a different kind of evidence, but only after you check what sold and how the price is reported.
Separate active, ended and sold records
Keep current offers in one group and records identified as sales in another. An ended listing is not automatically evidence of a successful transaction. Read the platform's status labels and documentation rather than inferring a sale from a page that is no longer active. Save the date of your research because availability and displayed information can change.
Check whether the displayed amount is the accepted price or an earlier asking figure. For example, eBay says its Product Research service can show actual sale prices when a Best Offer was accepted. That distinction matters when an ordinary result does not reveal the negotiated amount. If you cannot establish the actual figure, mark it unknown instead of treating the visible number as confirmed.
Match the object before comparing the number
Compare edition, language, scale, reference, completeness and visible condition. A boxed example with documented accessories is not directly equivalent to an unboxed copy missing parts. For cards or coins, a label or grade may also distinguish the offer, but it does not make every similarly labelled object identical. Retain photographs or a description sufficient to explain why you included the comparison.
Exclude obviously different versions and keep uncertain matches in a separate group. It is tempting to choose the highest result when selling and the lowest when buying. A consistent inclusion rule avoids that bias. Write the rule before selecting examples, such as the same reference, same packaging status and a broadly comparable documented condition.
Put prices on a comparable basis
Record currency, sale date, item price and stated delivery separately. Note whether taxes, premiums or other charges are included or unknown. Do not add an estimated charge and then present the result as a documented total. For a lot, record the number and identity of included objects rather than dividing automatically by the count.
If currencies differ, keep the original amount and state the conversion date and source when making a comparison. A converted figure is a calculation, not the price recorded by the original transaction. Similarly, an old sale reflects its own time and circumstances; it is not a promise that a comparable object would sell for that amount today.
Look at the range and the missing information
Several reasonably matched records are more informative than one striking result. Note the spread and investigate unusually high or low examples. A large difference may reflect condition, a bundled accessory, unclear reporting or something you cannot determine from the archived listing. Do not remove an inconvenient result without recording why it was excluded.
A small sample remains a small sample. If only one uncertain comparison exists, say that the evidence is limited rather than producing a precise average that looks authoritative. Repeated appearances of the same object should not be counted as independent sales without checking the records. Your spreadsheet can show uncertainty instead of concealing it behind a neat number.
Use the research for a bounded decision
For a buyer, compare the documented offer with your budget and collecting purpose. For a seller, use the research to choose an initial asking approach while recognising that demand, presentation and transaction terms differ. Neither use turns historical data into a guaranteed sale price or an investment forecast.
Keep your comparison notes with their sources and dates. When you revisit the question, update the evidence rather than recycling an old conclusion as current market value. If the transaction requires a formal valuation, insurance assessment or specialist appraisal, use an appropriate professional service with a clearly defined scope.
