Scarcity
Items that are in short supply or only available at certain times are seen as more valuable/desirable. What deadlines or limitations exist for your products? Are there bonus gifts you could offer for a limited time, or variants that you could present as a limited edition? ‘Last few remaining’, ‘while stocks last’ and ‘limited stock’ can all create urgency.
From Influence: The Psychology of Persuasion by Robert B. Cialdini