For various reasons I've decided eBay will be the guinea pig for trialling tracked postage only, starting from tomorrow (my shop has been closed over a week, so this will be interesting) - I'm posting about it here because a lot of my items are low value ($4-$7), and just thought there might be some sellers with similar business structures who could be interested in the end results (whether it be a success or failure etc), in which case I'd follow up in a few weeks, and again in a few months.
If there's any specific info or stats someone would be interested in knowing, let me know so I can keep track of it.
A couple of things to note, in case it puts any subsequent info I post in the right perspective, while I do get a lot of single-item purchases, the core of my business is multi-item purchases from repeat customers; which is something I expect would make the higher postage cost a little easier to take (postage is going from a bit over $3 flat rate to a bit over $6 flat rate).
I've also set up a discount for orders of $50+, so this may have an effect on some of the changes in buying patterns (if I still get any sales, anyway 
).
Lastly, some of my buyers are quite aware of the other platforms I sell through, and I won't be making any changes on those as yet, so this may result in decreases on eBay, but increases elsewhere (if I detect a significant pattern of that, I'll note it here when I update for anyone interested in that kind of stat).
If no one is interested, all good, and we can carry on as though you din't see nuthin' here. 
I have to admit I did a double take when I saw digital*ghost as the OP -
my immediate thought was what in the he!! could any most of us know that digi doesn't
I think during last year's peak boom was probably the best time to have tested it, but if I'm being honest I'm kind of hoping this will make my workload a bit more manageable, and maybe even my website a bit more attractive (I have untracked options there, but it's set up so that once the order reaches a set level, only tracked options become available). This does mean for the stat nerds (of which I count myself as one, albeit a dabbling one, so it's a term of endearment ) there's some bias in my experiment.
i.e. eBay is the biggest source of stress for me ATM, so if it reduces certain types of orders, and especially reduces post-sale handholding that so often seems to be required for those orders, I'm personally going to consider it a success, even if I take a hit financially 
- at the same time, however, there are a lot of similar businesses that charge $9+ for parcel shipping, with items starting from less than $1, who do really well (one of them - not on ebay - was doing so much business last year their handling time shot up to 2 weeks), so only time will tell how this will go down.
Day 2, or approximately 17 hours after re-opening with tracked-only postage options...
Just kidding, this isn't an real kind of update - I just wanted to say it was kinda weird to only have one package being posted going untracked when normally more than half are (the one untracked was placed via the website, all other orders off-eBay selected express or paid for the upgrade voluntarily). For some reason I felt a little bit like Oprah this afternoon, despite it not being through any benevolence of mine lol.
"You get a tracking number, you get a tracking number, everyone gets a tracking number!"
Which is just to say, sales did start trickling in despite the jump in cost, none have been for only one item as yet, per se, though there've been a few that are just 2x 1 product. So yeah.
Spoiler
Lame - I know, I know... 
