* Rarity: These books were popular and widely printed. While they might be considered vintage, they aren't necessarily rare collectibles.
* Condition: "Good condition" is subjective. Are there any tears, stains, or significant wear and tear? This impacts value greatly.
* Market Fluctuations: The value of used books fluctuates based on demand, current market trends, and even the time of year.
To get an idea of value, try the following:
1. Online Marketplaces: Search for similar sets on eBay, Amazon, or other online marketplaces to see what they are selling for.
2. Bookstores: Visit local used bookstores and ask about the value of similar sets.
3. Professional Appraisers: If you're considering selling the books for a significant amount, consult a professional book appraiser for a more accurate assessment.
Remember, the value is ultimately determined by what someone is willing to pay for them.