Anyone have experience or ideas for validating demand for a webshop *before* investing in stock?

I am looking to start up a web shop selling homewares (throws, cushions, candles etc.), but would like to be able to gauge how much interest there would be in the products I'm sourcing. I'm trying to get better at testing ideas before throwing money at them, but I'm not sure how to do this with would-be customers online.

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