Can I ask for a deposit that only becomes non-refundable after certain conditions are met?

Yes — structuring a deposit so it starts refundable and becomes non-refundable only once specific conditions are satisfied, such as the expiry of a due diligence period without a problem being raised, is a common and entirely negotiable approach. It gives the other side comfort early on, while diligence is still ongoing, and gives you increasing security as the deal progresses and their commitment becomes more concrete.

There's no standard version of this structure required by law, so the specific conditions triggering non-refundability need to be defined clearly rather than left general — what exactly counts as diligence being "satisfied," whether specific milestones need to be met, and what happens if a condition is only partially satisfied. Vague drafting here is exactly what turns a sensible, graduated structure into a dispute about whether the triggering event actually happened.

If this kind of graduated deposit fits your deal, put the specific conditions and dates in writing rather than relying on a general understanding of when the money becomes non-refundable. A Treadstone business lawyer can draft those conditions precisely so both sides know exactly where things stand at each stage.