I did a column on this:
https://adamstevenwarshaw.substack.c...ayagot?r=ff7k7
A pertinent excerpt:
The comparison shoppers, or as I call them, the comp bandits...you know them, the guys who search their phones and announce that an example the card you have ticketed at $50 sold a month ago for $40. I run into this all the time and my answer is usually "that's very interesting, thanks for the information. I think you should buy it on eBay." Gets some real head-scratching in response, so let me dig into it.
With rare exceptions, a comp bandit is deluding himself if he thinks he is educating me on price. I already know what my items are worth, which is how I priced them—and I price everything I put on my table. ...
Another consideration is how the comp has to be adjusted for context. The comp bandits don't think about what an eBay comp represents. A sale online and in person are not the same, especially in lower priced cards. The financial reality is that most buyers at a show are already enjoying a substantial discount over the online cost to them simply by taking shipping out of the equation and having sales tax folded into the price, so the online comp is more of an apples to oranges comparison. When I price cards for sale, I check comps on eBay and I factor in the shipping cost and taxes as a component of sale. A $1 card with a $4 shipping cost is really a $5 card, not a $1 card, so coming at me with a $1 comp and demanding the card for a buck is not a fair or honest comparison. I prefer to think it happens because a substantial majority of collectors simply forget the shipping costs and sales taxes when looking at an online price, especially if the data scraping app they are using doesn’t add shipping to the costs, but that’s just me, lover of humanity (insert roll-eyes emoji here).