Can I add a wee bit to that?
# First off lay your fleece out somewhere very clean (new tarp) in the sun, cut side up, for half an hour to dry. Sheep are quite sweaty and damp fleece stores badly.
# Crawl round the whole fleece and pick off all the daggy and draggly bits. As well as the backside, the neck wool is often completely full of old hay trash, so if it is, just pull the whole bit off, wool and all - it's never going to be workable if it's bad.
# You might as well check the staple quality while you're there. Take out a small staple of wool (a bit which is held together by the tips). Hold each end tightly in your hands, hold it near your ear, then snap your hands apart. This should make a nice twang. If the sound is soggy, and the staple tries to pull apart, you have a weak staple which won't sell. It could just be that the shearer has shorn below the 'rise' so check it carefully.
# Lay your fleece cut side down, make it as neatly oblong as possible, fold in a third along each side, then roll up from the tail end towards the neck. For fleece for selling, don't do this tightly (as you would for the BWMB) as when a hand spinner looks at the fleece they will want to open it up, and for it to be light and lofty. I don't twist and wrap the neck wool round the bundle, as the neck wool can be really fine, and twisting it makes it more difficult to prepare for spinning.
# I store mine in new woven polypropylene sacks - you sometimes get these with feed in - turn them inside out before using. Pillow cases are great too for smallish fleeces, anything with absolutely no access for clothes moths. Stuff your fleece in neatly and tie very tightly at the neck. Never use polythene bags.
#Hang up in a dry, cool place with a through draught, no sun as this degrades the polypropylene. Never store bags of fleece on a floor, or anywhere damp.
When people are viewing your fleece, whether at your home or elsewhere, they will probably want to unroll it for a proper look. I'm in two minds about this: I would always want to examine any fleece carefully, but a fleece which is unrolled more than, say, three times is going to start falling apart, so think how to deal with that. Other buyers are happy just to squeeze the sack and take a small staple from the top of the bag to look for quality.
There are a lot of Shetland fleeces out there for sale, so you may have difficulty finding buyers, but don't give up.
Have a close look at your Kerry Hills too, especially any first shears. That's far more unusual, bigger too, so if you have some good ones it would be worth hawking a couple of those around with the Shetlands.