1. Identify every holding
Record set, card number, language, printing, condition and quantity. Separate reverse holos, regular holos and special promos. Include grading company and grade for slabs. Duplicate entries and wrong variants can distort the total more than small daily price changes.
2. Choose a valuation basis
Choose a market and currency. A Cardmarket reference and a converted US price do not necessarily describe the same selling opportunity. Record source and date. Missing prices remain unknown: they do not mean zero value and should not be replaced by an arbitrary similar card.
3. Separate market value from proceeds
Suppose 20 cards add up to a €500 reference value. An illustrative 15% discount for selling the whole lot gives €425 before other costs. That discount is an assumption, not a market rule. Selling individually may bring more but requires time, buyers and separate shipments.
4. Read changes correctly
A higher portfolio total can come from new holdings, corrected identification or updated prices. Compare the same holdings on the same valuation basis. Investigate unusual jumps in individual cards before interpreting them as a market-wide trend.