How do you guys value and sell rivens?

Check if the weapon is meta, goto warframe market, price mine 1 plat cheaper than the cheapest if it has garbage rolls.

If good rolls are present i will price it mid range and drop it 50 plat weekly till it sells.

To me plat in hand is worth more than some potential higher price down the line.

I base it sorely on my knowledge of the weapon, it's theoretical placing in the current meta, and what stats the Riven has or if it is unrolled.

So, for example, if I get a Veldt Riven, I'll be happy to sell it for 10 if at all, but if I get a Kuva Bramma Riven, even unrolled can go for a few hundred.

As for stats, a lot of people are idiots who just flock to the CC, CD, MS stats regardless of the weapons Riven Disposition and will pay or demand massive amounts of Platinum for them but will instead completely misjudge a value of a good QoL Riven on a low Dispo weapon. They also don't understand the impact of some of the negative stats. Having -60% magazine size on a bow has absolutely no effect but some people will be convinced this makes the weapon unusable. Likewise, some will claim -Zoom is harmless but then don't realize it's for a Incarnon weapon that needs headshots so this makes it harder to aim with.

I would say -Zoom is harmless, even on Incarnons. Headshots aren't that hard to get, you can do it with hip fire. Heck, most of the time -Zoom is a benefit unless you're trying to fight at really large distances in the open world or something, but that's a highly specific scenario that you don't have to engage with.
- Your reply is actually a good example of user variety. I wouldn't pay a single dime for a -Zoom Mitter Riven because I wouldn't be able to hit heads as easily anymore but it might not be an issue for you so your value for the same Riven will be quite different.
  
  This is important to know for OP because one man's trash is another man's treasure and vice versa.
I feel like those 3.X punch through rivens are undervalued. Most people ignore 1.0 punch as its onyl use is for like shield guys. once you start getting like 3+ you can shoot through most objects.

I only know that some similar rivens might be found on warframe.market and you can derive a baseline price range.

For individual evaluation I have no clue

Oh also I sell them ( I didn't do it a lot) through warframe.market

If that wasn't clear lol

If a Riven has 'perfect' stats (aka 3 of the best stats and 1 negative that doesn't matter for the weapon or can even be a bonus like -zoom) it is naturally very valuable. However, this value of course depends on the weapon it is for, with more meta weapons making it a more valuable riven.

The Riven's value decreases significantly if you don't have perfect stats, and the farther you are from perfect stats the worse value it becomes exponentially (it is very easy to roll at least 1 good stat).

I sell my Rivens veiled. I asked in r/Wartrade prior to the blackout about pricing (though Wartrade doesn't seem to be participating).

IIRC pricing is as follows:

Shotgun, Rifle, Melee: 15P

Pistol, Zaw: 5P

Generally mine well sell in a few days to a few weeks on Riven.market with occasional mentioning in trade chat that I've got Rivens for that price. I've had a few people try to negotiate, or scam, but holding firm to my prices I've yet to have a negotiator decide no deal.

I have no idea how to price unveiled rivens and won't speculate seeing there's people here already explaining how they would/do it.

Know what weapons are popular, or at least good. Also which are new, and which are popular as stat sticks. Conversely, know which weapon types aren’t worth anything. Hint: Kitguns and Zaws.
Know what stats are good on the weapon your riven is for. Crit chance is terrible on the Embolist, for example. Status is bad on a rubico.
Put together a combo of good stats and popular weapon.

The most expensive rivens seem to go to Vectis and Rubico rivens, but there’s always a peak of price whenever DE buffs a weapon. Ocucor rivens are super hot right now because of Sentient Surge being in Nightwave, and I expect to see a bump in interest for the Battacor, which has a mod in nightwave coming up.

Personally, I don’t want to entertain PMOs, so I always list my price in trade chat. I do add a filter for whatever weapon I’m trying to sell a riven for, to get a sense of how many other riven sellers are out there. I start a little high to make sure I’m not undervaluing it out of the gate.

Weekends are better for selling.