Customers asking for Titanium will accept anything you give them, provided it is a lower quality (and price range within their budget) than Titanium.
Example
Customer asks for Adelite Greatsword
You already have an Iron Greatsword on hand.
You can hand them the iron Greatsword, You won't get a "Customer Type" (Customer's Type) bonus
You cannot, however, Exceed their price range. If they ask for Copper, You must give them Copper, They cannot afford Tin or better - Logically.
Example again - 1 Titanium ingot is 100 gold, If they ask for a Titanium Greatsword - They're prepared to spend around abouts 400gold give or take.
They can afford anything under 400 gold.
If they ask for Iron Greatsword - which is like... ridiculously less than that, They won't be able to afford even a Titanium dagger, Let alone a more expensive greatsword - heck they probably can't even afford an Adelite dagger.