Jarred tobacco transactions are tricky and require a leap of faith on the part of the buyer. I’ve always thought it’s a bit like buying wine that’s been decanted and poured into a mason jar. How do you know it is what the seller says it is? So obviously much depends on the reputation of the seller and the risk profile of the buyer.
Having said that, I think you can bifurcate the problem into two parts: selling blends that are still pretty readily available from retailers and selling those that are scarce; either in production but very difficult to obtain (think Esoterica), or out of production entirely (think McClelland and every unicorn you’ve ever heard of).
For the readily available blends as a general rule I’d assume most sales take place at a large-ish discount to what a retailer charges, with aged tobacco perhaps receiving a smaller discount. Why? Because the buyer always has the alternative of getting guaranteed product from a retailer, perhaps with free shipping if the purchase is large enough. Resellers have to offer a big enough discount to persuade the buyer it’s worth it to buy unverified tobacco from them.
For the out of production stuff once again I’ll parse the question into two pieces: tobaccos that were available in tins and tobaccos that were only or mostly available in bulk (think 5100, 2015, etc). For the former again the buyer is purchasing something unverified that he could buy verified if he was willing (and able) to buy a tin instead, in which case the question of authenticity is addressed. So I would again expect a discount to the current market price (not retail, but some blended average of Pipestud and TinBids) of tinned product. Here the discount might be a bit smaller because of scarcity and the volatility of the secondary market.
Finally, as for tobaccos that were only, or even primarily, offered in bulk (McClelland is the prime example here, perhaps along with a few others, eg Motzek Strang, Comoy casks, etc) pricing is much higher despite the uncertainty because these tobaccos tend to be very rarely offered. In most cases they were either originally often considered as blending components and used as such, or always occupied a very niche position in the US market (ie the volume sold here was, relatively speaking, negligible). In both cases the amount lying around today is small.
And note that for this last category the issue of trust is mitigated by the simple fact that the buyer has no alternative. These were bulk blends ab ovo; if you want them you accept that fact as a condition of your search and understand your only option is to buy unlabeled tobacco. Your best and only guarantee is your assessment of the seller’s reputation. In such cases where demand is high and supply low tobacco is priced accordingly, typically at a multiple of the original cost, just like Esoterica.