In order to make the listing process a bit faster and easier I created a pricing spreadsheet. This spreadsheet tells me what I should price my items at on Ebay and Mercari depending on what price I used for Poshmark. Keep in mind that I always price my items 20% higher than I actually want to sell them. This price buffer is lowered to 10% for the Ebay pricing when buyer pays shipping. It is kept at 20% when offering free shipping on Ebay and is kept at 20% for Mercari pricing. It also incorporates the varying fee structures of the different platforms.
This spreadsheet also has different columns for pricing depending on if you offer free shipping or have the buyer pay shipping. The listing price is higher if you are offering free shipping in order to cover shipping costs. Poshmark does not have a free shipping option so they only have one pricing column.
For Ebay I also have best offer automatic accept and decline prices. This prevents lowball offers and saves me time. The only time I have to interact with an offer is if it is between my accept and decline prices. I currently am using a buyer pays strategy on both Ebay and Mercari and am experimenting with 7 cent ending on Ebay prices.
Here is the link to my pricing spreadsheet for informational purposes: https://docs.google.com/spreadsheets/d/1vMhPj-m7viRE_U_N1vcB2Xs_PRHLHajH0wTp39-VKmE/edit?usp=sharing. Feel free to make a copy and adjust to best suit your needs.