Watch winder, service, polishing, regulation, how do cart add-ons work?

Two patterns, depending on what you offer:

• Physical add-ons (watch winder, travel case, leather strap upgrade), standard Magento configurable / linked-products. Show in cart with one-click add. Watch winders are the highest-attach: $300 (single-watch automatic) to $3,000 (8-watch climate-controlled cabinet). ~22% attach rate on $5k+ orders in my data.
• Service appointments (full service, polishing, water-resistance regulation), bookable from product page or post-purchase email. Customer picks a service tier, sees the lead time (Rolex full service is 6-14 weeks legitimately; tell them upfront), pays deposit, ships in via prepaid Brinks (declared at lower service-value, not original purchase). Magento manages it as a service-SKU order with a longer fulfillment SLA, status moves through booked → received → in_service → completed → shipped_back.

Critical for pre-owned dealers: the service revenue compounds and locks the customer into your shop for the watch’s 30-year life. A Rolex sold today comes back for service 3-5 times over its life, each at $800, $2,500. If you build the platform to remember “this watch was sold by us in 2024” and email the customer at the 5-year service mark, your service-revenue retention is 60%+. Most dealers leak this entirely.

Pricing transparency at booking matters: post the service-tier prices publicly, post the lead times honestly. Customers Google the comparison and reward the dealer who isn’t hiding the 14-week truth.