Wouldn't you say that's the general consensus if the work is considered important ?
The British museum paid for most of their artworks. Granted, probably not what they were worth, but certainly a price the sellers were willing to accept.
Who's to say "what they were worth" at that time and in that place? Pretty much the only indication we have is whatever price the buyer was willing to pay and the seller was willing to accept.
We might consider them "priceless" objects in a museum now, but that doesn't tell us anything about what they were worth at the time of acquisition. The "value" of an artwork is almost entirely a cultural construct, not something inherent in the object, and may vary drastically across both time and space.
The British museum paid for most of their artworks. Granted, probably not what they were worth, but certainly a price the sellers were willing to accept.