People will not know what they are buying ..they will only know what BCS graded them at.
Couldn't have said it better.
Third party graded notes in less than top grade sell for less than catalogue because people don't trust the grading. Plain and simple. Even people who don't know how to grade for themselves will assume that the stated TPG grade is too high, and they will bid lower to compensate for a perceived margin of error. It doesn't matter how "conservative" a company is reputed to be because every company makes mistakes and logic tells us that undergraded notes are removed from their holders while overgraded notes will be forever locked in their plastic tombs, meaning that the available population of notes in a certain TPG's holder will gradually become less representative of the company's grading standards over time. Furthermore, every company out there will only issue opinions on technical grade. They don't evaluate appearance because there is no grading scale for appearance. We've all seen incredible examples of notes that look far worse than their assigned grades. This one is probably in everyone's top 3 of worst graded notes...
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Once a note is slabbed, the few collectors in existence who are confident with their grading skills are essentially locked out. I need to examine a note's surfaces to determine its true state of preservation, and this means holding the note up to light at an angle. Can't do that with a note in a highly reflective slab. I know there are people who say they can grade a slabbed note, and I would love for them to explain their technique. Since I can't grade a slabbed note for myself and since sellers of slabbed notes don't take returns, there's no incentive for me to take a risk on a note based on someone else's opinion. Most of the time, I don't even bid on slabbed notes because I know my bids will be too low. I subscribe to "bigger idiot theory" (BIT) which tells us that the only way you're going to make a profit on an overgraded note is to find a bigger idiot. Slabbed notes represent the pinnacle of BIT, meaning they are overgraded to the very edge of credibility, and even people with no idea how to grade are not going to believe a higher grade even if you take the notes out of their slabs and try to sell them raw.
As for the safety of graded slabs, we've already discussed this as it related to BCS holders which the company admits contain PVC...
http://www.cdnpapermoney.com/forum/index.php?topic=10287.0