Rich (and all), the problem I always have in estimating shipping costs is:

One, and only one, postal clerk at a particular post office charges me only $0.98 to send out a chip in a padded mailer. And she is not always at her counter, or she's busy with someone ahead of me, so I have to go before another clerk - and pay $2.32. Same mail class, and I have no idea why! And if I sell to someone outside of the USA, the international postage rate . . . could be anything! That is why I feel I can never offer "free shipping." In some instances, particularly where my actual shipping is considerably less than estimated (say, $1.50 rather than $3.50 pre-charged), I will gladly offer a refund via PayPal. I also offer combined shipping which buyers usually appreciate.

Also remember, I must factor in my cost for the mailers and a tiny bit for the invoice included inside the mailer. Bean-counting, but this would be totally out-of-pocket if not included. I do not make very much profit, usually, by eBay sales (remember too the eBay listing fee plus PayPal acceptance charges that nibble away at the earnings).

Having said all this, though -- $4 shipping or some such for just one or two chips . . . seems a bit high!