If a new reseller (or seller) reaches out to me for advice, one of my first tips is to invest in a cheap but good quality scale. I have made SO MANY mistakes with shipping in the past, and those issues flew completely out of the window when I bought a scale.
If you sell a lot of the same item, you can weigh it once, calculate the shipping, and you’re done forever. If you sell lots of different items, you can weigh them as you list, or just get a general idea of how much it costs to ship things pretty darn quickly. I undercharged and overpaid for shipping sooooooo often back in the day, I’m almost embarrassed to talk about it. Almost. 😂
A scale doesn't just save money, it saves time too. If you have your postage label printed, you can drop off your parcels at the post office or schedule a pickup with USPS!