The live preview is the first thing most buyers click, ahead of the description, ahead of the screenshots. It is the closest they get to using the thing before paying for it, and it is the part sellers maintain least.
A demo that is down is worse than no demo
No demo reads as a choice. A demo that times out reads as an abandoned item, and the buyer applies that judgement to the code as well. Check yours on a schedule, not when somebody complains.
Fill it with plausible data
Three products called Test, Test 2 and asdf tell a buyer nothing about whether your layout survives real content. Real-looking names, realistic quantities, a full page of rows, one long title to prove it does not break. This is where buyers decide whether you thought about the details.
Let them break it
If your demo is read-only, buyers cannot answer the question they came with. Give them a sandbox that resets, or an admin login with real permissions on data that does not matter. The reset is the part that makes this safe.
Keep it on the version you are selling
Demos drift ahead while you develop. A buyer who is shown a feature that is not in the download will file that as a refund, and they will be right to.
Show it on a phone
A large share of buyers open your demo on the phone they are holding. If it is unusable there, they have their answer regardless of what your description claims about being responsive.
