Recommendations

Two hops: from the product to its buyers, then to their other products.

MATCH (:Product {name: 'Tent'})<-[:BOUGHT]-(c:Customer)-[:BOUGHT]->(other:Product)
RETURN other.name AS alsoBought, count(c) AS customers
ORDER BY customers DESC, alsoBought LIMIT 3;

+----------------+-----------+
| alsoBought     | customers |
+----------------+-----------+
| "Camp stove"   | 2         |
| "Head lamp"    | 2         |
| "Sleeping bag" | 2         |
+----------------+-----------+
3 rows

Customers ranked by how many of Ada's products they also bought.

MATCH (me:Customer {name: 'Ada'})-[:BOUGHT]->(p:Product)<-[:BOUGHT]-(peer:Customer)
RETURN peer.name AS peer, count(p) AS shared, collect(p.name) AS products
ORDER BY shared DESC, peer;

+-------+--------+--------------------------+
| peer  | shared | products                 |
+-------+--------+--------------------------+
| "Ben" | 2      | ["Tent", "Sleeping bag"] |
| "Dan" | 2      | ["Tent", "Head lamp"]    |
| "Eve" | 1      | ["Sleeping bag"]         |
+-------+--------+--------------------------+
3 rows

Products her peers bought and she did not, ranked by how many peers bought them.

MATCH (me:Customer {name: 'Ada'})-[:BOUGHT]->(:Product)<-[:BOUGHT]-(peer:Customer)
      -[:BOUGHT]->(rec:Product)-[:IN]->(cat:Category)
WHERE NOT (me)-[:BOUGHT]->(rec)
RETURN rec.name AS recommend, cat.name AS category, count(DISTINCT peer) AS peers
ORDER BY peers DESC, recommend;

+------------------+-----------+-------+
| recommend        | category  | peers |
+------------------+-----------+-------+
| "Camp stove"     | "Camping" | 2     |
| "Hiking boots"   | "Hiking"  | 2     |
| "Trekking poles" | "Hiking"  | 1     |
+------------------+-----------+-------+
3 rows