Is it preferable to sell my own stuff locally into my own UK market using If so, what policies would be advisable to use (e.g. free returns, no returns, etc.)?

You should always accept and offer 30 day returns.

When you sell your own product on your eBay account, you can offer free shipping within the UK and a fee for US buyers. We believe it is best to always offer free shipping.

The shipping cost can be added to the price of the product.