ChipFlip
A used Steam Deck runs $350. A used Switch OLED with the screen model upgrade runs $234. Both are handhelds, both are current, and they're built for two completely different jobs.
Different buyers, different question
The Steam Deck runs full PC games through Steam and, with some setup, other PC storefronts too. The Switch OLED runs Nintendo's own library exclusively. Someone deciding between these two is really choosing between a portable gaming PC and a portable Nintendo console, not comparing matched specs. The $116 price gap reflects that difference more than it reflects which hardware is stronger.
Where the Deck earns its price
Access to a massive existing PC game library, including titles the buyer may already own, is the real value here. Valve's hardware also gets regular software updates that keep expanding what runs well on it. For someone who already has a Steam library sitting unused, the Deck gives you access to that catalog on the go.
Where the Switch OLED earns its price
Nintendo's exclusives don't run anywhere else. If the buyer wants Mario, Zelda, or Pokemon specifically, there's no PC alternative that replaces that. The OLED screen upgrade over the base Switch model also matters more here than a spec sheet suggests, since handheld play means staring at that screen for hours.
The resale angle
Battery health matters on both, but it matters more on the Deck given its higher power draw running full PC games. Ask about charge cycles or battery replacement history before buying either one to flip. A degraded battery quietly eats into resale value on both platforms even when everything else checks out.
Bottom line
Which library does the buyer actually want access to? That question decides this more than any spec sheet does. Price each one against what it's built to do, not against the other directly.