Trade-in + sell-to-us flow, how do you quote a Submariner in real time?

Chrono24 and Bob’s Watches set the bar. The flow:

1. Customer enters Reference # + year + condition + box-and-papers, e.g. Rolex 126610LN, 2023, mint, full set.
2. System pulls a guideline quote from a market-data feed, options: WatchCharts API (~$500, $2k/mo for B2B data, most accurate for popular references), Chrono24 IndexData (free index but limited reference coverage), in-house data from your own sales history (best long-term, requires >1,000 transactions/yr to be statistically useful).
3. Instant guideline shown with a disclaimer that the final offer depends on inspection. Typical guideline accuracy: ±10% of final offer.
4. On accept: prepaid Brinks/Malca-Amit label generated + insurance attached. Customer ships in.
5. Authenticator inspects, photo / video pass, movement check, water test, box-and-papers verification.
6. Final offer issued, within ±10% of guideline if condition matches. If condition is below stated, revised offer with explanation + photos.
7. Customer accepts → ACH payout (2-3 business days) or store credit with 10% bonus (drives reuse, ~40% take rate in published data).

Magento custom module manages the entire flow as “reverse orders” with their own state machine (quote_requested → quote_accepted → watch_received → inspected → final_offer_issued → paid_out). Build cost: ~$15k, $25k. Pays for itself in 90 days if you do >$30k/mo in trade-ins (acquisition cost is ~30% lower vs auction sourcing).