The lines, and which is which
Vanguard and Luxx are the premium lines and the reason most people buy Selkirk: a soft, connected feel at the ball and control that rewards touch rather than handing out free power. These are the ones worth seeking out secondhand.
Amped is the older premium line. Honest paddles, still perfectly playable, but several generations back on face technology, which matters if you rely on spin and matters much less if you do not.
SLK is the budget line and it is worth being direct about this: it plays like a different company made it. That is not a criticism of SLK at its price, but somebody buying used specifically because they want the Selkirk feel should know the badge alone does not deliver it.
What wears, and what only looks like it does
Selkirk edge guards take scuffs early and take them well. A chewed guard on an otherwise sound paddle is the single most overweighted defect in the secondhand market, and it is exactly the kind of cosmetic wear a grade should price rather than disqualify.
What actually matters is the face across the top third, where mishits land and where a thermoformed Vanguard or Luxx shows its wear first. Run a thumb across it and feel whether it still catches.
The thermoformed generations need the same perimeter tap test as any foam injected paddle. Selkirk's build quality is high and failures are less common than average, which makes it more important rather than less to actually check. An assumption of soundness is how an unsound one gets through.
Shapes, and who each one suits
Selkirk sells most of its premium lines in more than one shape, and the shape matters more to how a paddle feels than the line name does. The standard shapes are wider with a large central sweet spot and are the forgiving option. The elongated versions trade that width for reach and leverage, with a sweet spot that narrows and moves toward the tip.
This is worth attending to when buying secondhand, because two listings can carry the same model name and play quite differently. The shape is on every listing here, and it is the specification most worth matching to the paddle you already know you like.
If you are coming from a wider paddle and are not certain, take the standard shape. Reach is easy to appreciate in a shop and harder to live with on a paddle you miss the middle of.
Why so many reach the secondhand market
Selkirk is the brand most players trade up to, which means it is also the brand most players trade up within. Somebody who buys a Vanguard and then decides they want the elongated version has a perfectly good paddle to move on, and that is a large part of what fills this part of the market.
It also means the supply skews toward well cared for paddles. A paddle that somebody bought deliberately, at a premium price, after doing research, tends to arrive in better condition than one bought on impulse.
The practical consequence for a buyer is that Selkirk stock moves quickly here. Every listing is a single physical unit, so the one you are looking at is the only one of it.
What to buy at which grade
A Vanguard or Luxx at Like New is the sweet spot of the whole Selkirk secondhand market: the feel is intact, the wear is cosmetic, and the discount against retail is real.
At Excellent, buy for fit rather than for performance. It is the cheap way to find out whether you get on with a Selkirk shape before committing.
Mint is worth the premium on a current generation Vanguard or Luxx, because on these the face texture is most of the paddle and Mint means it is essentially intact.