Thanks for the info, digital*ghost. I had considered just having a flat shipping rate, as my items are tiny and would work well with, say, $1.50 max. postage. I have just been a bit nervous about changing 100 listings in bulk. (Not that doing so would solve the problem of eBay not combining items onto one invoice, as far as I can tell - because all this happens before any invoices have been sent, as far as I know.)