In order to sell items - You need to have a hammer.
What you start with is copper hammer - you sell only copper.
If you make a tin hammer - you sell tin and copper.
If you make a Titanium hammer - you sell any metal in the game.
There's a bit of a "WIP" here though - Due to Alloys being so new.
Brass (Haven't found zinc, but Brass ingots can be obtained for a certain place on the map)
Bronze
And Steel
All will unlock selling more advanced metals than what you currently have.
They will /at least/ ask upwards of Mithril - but it's possible that all 3 alloys will have customers ask all the way up to titanium - The alloy hammers seem to be registered "Above all other metals"
The Alloy picks work seemingly as intended - Brass Pick will only mine up to a certain level - Bronze up to Adelite I believe, maybe only Iron - Steel will mine up to Mithril
Customers that request Alloys (don't exist) - except they technically do - When You have an Alloy Hammer, you'll occassionally have a customer come in asking for "Blank" tool/weapon - No specific Metal is given.
They're actually Asking for Brass, Bronze, Or Steel, At least, they seem to be.
Depending on what they're asking for, You may be able to sell them anything under the sun.
If they're asking for Steel (Seemingly) they'll accept Anything.
If they're Asking for Bronze (Seemingly) they won't accept titanium but eventually they will accept /something/ you can give them, and above Copper.
Brass has the worst options - Seemingly being restricted to Tin or Copper only.
If the Customer asks for "Blank" Tool "Specific Grip/Tool head" - Send them away.
They will only give you exp and be worthless to you. - They will only accept whatever they are asking for, which you cannot hope to fulfill, and even if you managed to fill the order - Alloys are So new, They have no value registered, So they sell for nothing.
It's possible that there's a bit of mixed signals here - and that the "Blanks" are what is supposed to be the "alloys" and the "Alloys" are "separate" thus if you ACTUALLY sold a "Blank" - you'd "actually" sell that specific alloy and actually make a profit - but because "Alloy" somehow is separate and has no price - you sell "Blank" instead..... if that made sense...
Anywho.
Customers will buy what is in their price range - Unless - They specify extensions. - in which case they will /only/ accept what they asked for.
Example
A Customer asks for a Mithril Greathammer.
You can give him an Iron Greathammer, No problem.
You cannot give him an Adamantine or Titanium Greathammer - As these are more expensive.
If a Customer asks for a Mithril Greathammer with a common grip and a large hammer head
You must give him a Mithril Greathammer - The grip/head I believe is negotiable, with the loss of a specificity bonus (10%) - but it /must/ be Mithril.
If you only have an Iron Hammer equipped - They will only buy Iron, Tin, Or copper, Never will they ask for something "More expensive" than your hammer - which is what makes Alloys "Oddities"