Upsell and cross-sell
Upselling means offering a superior version of the same product; cross-selling means offering a complementary product. Both techniques increase basket value without adding customer acquisition cost.
In practice
At contract signing for a monthly SEO retainer, the account manager offers a discounted backlink audit add-on: that is cross-sell. When a customer reaches 80% of their tracked keyword limit, an in-app alert suggests the next plan up: that is upsell. Combined, these levers drive MRR expansion and reduce dependence on new acquisitions to hit revenue targets.