Quoting the Domino Box

An interviewer slides a sealed box across the table: a standard double-six domino set, every tile distinct. "Make me a market on the number of tiles inside — then tell me the exact fair value." A double-six set contains every possible tile whose two ends each show between $0$ and $6$ pips, with no tile repeated. How many tiles is that, and how should you quote before you've worked it out exactly?