Us too
JesterPoet said:We use a system of "If it is an expensive or rare component you need to prove that you can provide it, but if it is common and/or cheap, it's assumed you keep a supply in your component pouch"
Our rules for what is rare/expensive are pretty arbitrary, but nobody has ever had a problem with them. A 100gp pearl for the identify spell is probably the best example of a common component that you need to prove you bought on a regular basis.
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We also use a similar system, where components are assumed to be on hand unless they are extremely difficult to find. I as the DM modify the treasure recovered to 'assume' most of these costs and make it easier on the players. We do they same thing with normal equipment. The players simply notify me that they are buying a new backpack, or coil of rope, flask of oil, trail rations etc. In early levels when characters are extremely poor they must provide money for such purchases but later we just don't bother.