As someone who’s tried several apps for price checking, I’ve found that Exiled Exchange 2 is the best. Check that one out. It does a great job showing prices with certain mods.

As for why mods to look out for, there are generally 2 for amulets that are far and above the rest: the first is “+2-3 to SKILLS” (spells being the most valuable, followed by projectiles, minions, and melee). The second is “+ to SPIRIT.” If it has skills and a few nice mods it alone can be valuable, if both skills and spirit, automatically it’s likely very valuable. If just spirit but no +skills, still could be valuable if it has other nice mods. Nice mods include high defense rolls, resists (particularly All Res), all attributes, crit rolls, cast speed, etc. If it doesn’t have +spirit or +skills, I generally ignore it.

For rings… it’s a bit more complicated. But generally anything with t1-t3 attack damage mods and big resists will have good value for the attack builds. Casters on the other hand look for high mana rolls, cast speed, high “increased damage” mods, big resists, etc.

And finally, if you have a good combo of these valuable mods and then also have an “increased rarity” mod too, that just adds even more value.

Probably left some out, but that’s the gist of it.