I've been there and done this.... actually, it's the bread and butter of the business I run.
What I'd suggest is this;
- Go to the An Post site and check the different post services available to Ireland, with prices, size limits etc.
- Look at what you are selling and try to come up with a few "standard" type packaging types and weight.
- Work out what it'll cost you in postage.
- Then look at international destinations and do the same. It's almost certain you'll be able to break it down into UK, EU, Rest of Europe, North America and one or two "Rest of World" zones.
- I don't know how similar Irish eBay is to the UK site (a lot of Irish sellers actually sell direct on the UK site as well to access a larger market), but their shipping is a bit of a mess to set up. You should be able to nail it down to Ireland and a couple of international zones.
- The key thing is to offer the base service as Free Shipping by building it into your item price, so for example a £10.00 item that'll cost £2.50 to post will have £2.75 added to the price to allow for 10% eBay fees on the postage. Having a free shipping option gives you a serious boost in eBay search ranking.
- Then add any premium services (e.g. next day delivery) as an extra shipping method, but reduce it by the amount you've already built into the item price.
- Work out your "risk threshold" above which you want to send items tracked & signed for, and incorporate that into whichever service you use. Don't give buyers a choice at that point, they'll always go for the cheapest option because you're the one who will lose out if they claim non-delivery.
- For international orders, there are some places (Italy, France, most of Africa and the Middle East) where the buyer mantra appears to be "if I didn't sign for it, it must be free". ALWAYS send items to those countries tracked & signed for !!
Aaaand I should have just made this a post. Maybe I'll copy it, add a bit more detail and do just that 😁 But hopefully it makes sense ! After a very short time it'll become second nature. Excel is your friend.