I made a few corrections and additions to sjohnston's excellent potion identification flow chart, and added a section on scrolls.

I also included some guidance for prices that shopkeepers offer to you.

Follow the step presented, in order, until your item is identified.

Potions

* Is it "clear"? WATER * Did you get the potion from a nymph? : (probably) OBJECT DETECTION * (a)pply the potion. <Lights> : OIL ((a)pply again to unlight) * #dip an unneeded tool "(" into the potion. <transforms into another tool> : POLYMORPH (Uses up the potion) * #dip a non-poisoned missile weapon into the potion (in case you have no unicorn horn, or want poisoned weapons) <Coats weapon>: SICKNESS (Uses up the potion) * #dip a unicorn horn into the potion <Turns clear>: was HALLUCINATION, CONFUSION, or BLINDNESS; now WATER <Color changes>: was SICKNESS, now FRUIT JUICE * #dip amethyst (or violet gems that might be amethyst) into the potion <Changes color>: was BOOZE; now FRUIT JUICE; (gem is AMETHYST) * (d)rop the potion in a shop. Offer price<A,B/C,D>[base price] POTION TYPE(s) ----------------------------------------------- < 2, 2 / 1, 1>[5] UNCURSED WATER < 25, 19 / 16, 12>[50] SEE INVISIBLE, BOOZE, SICKNESS, or FRUIT JUICE < 50, 38 / 33, 25>[100] RESTORE ABILITY, CONFUSION, HALLUCINATION, HEALING, EXTRA HEALING, SLEEPING, HOLY WATER, or UNHOLY WATER < 75, 57 / 50, 38>[150] BLINDNESS, INVISIBILITY, MONSTER DETECTION, OBJECT DETECTION, or GAIN ENERGY <100, 75 / 66, 50>[200] SPEED, LEVITATION, ENLIGHTENMENT, FULL HEALING, or POLYMORPH <125, 94 / 83, 63>[250] ACID, or OIL <150, 113 / 100, 75>[300] GAIN ABILITY, PARALYSIS, or GAIN LEVEL The first price listed is the most likely offer. The second price, after the comma (",") is offered 25% of the time. Prices after slash("/") are offered to tourists below level 15, and to anyone wearing a Hawaiian shirt or t-shirt. For ambiguous prices (75/50), repeatedly drop the potion until you see the other price. (sell prices for shop-owned potions are more complicated and not described here) * (q)uaff the potion in the following environment: (Uses up the potion) On a level with a sink (to land on after leviation). On a level that has both monsters and items somewhere. Lock yourself in a safe room with your pet, in case of paralysis or sleeping. After #dip-ping a unicorn horn. At full hit points. Not hallucinating. Non-cursed potions only. NOT wearing sustain ability ring. Avoid the most expensive category, to avoid wasting valuable potions. Most potions will auto identify when (q)uaffed. Use "\" command to see what the potion was. Others: <"This burns..."> ACID <"Ooph! This tastes like liquid fire!"> BOOZE <"This tastes like (fruit) juice."> FRUIT JUICE or SEE INVISIBLE <"Wow! This makes you feel good/great!> RESTORE ABILITY * If you get this far and have not identified the potion, I recommend waiting until you get a scroll or spell of identify. Or uncurse the potion with a scroll of remove curse. Throwing potions at monsters for identification seems too wasteful to me.

Scrolls