This came up a couple of times and people don't seem to understand equivalent value so I'll try to explain here.
When trading, the most fair way to compare value is by using the same metric. The default setting on deckbox is TCGMid. However, since deckbox doesn't automatically show TCGMid value for some things (promos, foils, sealed products, playmats, etc.), sometimes you have to look elsewhere to find an agreeable metric. TCG generally has values for foils/promos people can look up so that's usually a non-issue. However for sealed product/other things, eBay is usually the go-to because it is (usually) the cheapest place to get something.
Now to where I get into arguments: if we're using eBay for our baseline metric, the fairest comparison to eBay lowest BiN values (i.e. the cheapest value you can get a card) is TCGLow.
Compare some cards on eBay vs TCGLow:
Goyf
Windswept Heath
eBay/TCGLow value is around how much you can get if you were to sell your card to someone (on here, on eBay, to whoever except for stores) and you can then buy whatever card you want with that money. Since you will most likely want to get the cheapest deal you can, that will most likely be eBay/TCGLow value (outside of sniping deals on eBay/elsewhere). Put another way: you can't pay eBay in $140 Goyfs for anything. You have to sell the Goyf (or whatever card) first and then buy whatever. So in short, trading at eBay/TCGLow value eliminates that middle step but that is essentially what you're doing.
To reiterate: if you're wanting something (say a sealed FTV) at eBay value, don't value your cards at TCGMid for comparison because that is not the same metric.
/rant
