I went to Morocco last year (the whole of Jan, only for fossil collecting/buying) so I’ll answer as best as I can.
Most trilobites like this are usually found as lumps of rock with only a small section poking out at one end making it obvious- the cross section of a trilobite is pretty obvious if it’s only a partial (top one here, although this is a thin section view), or perhaps a little of one edge or a spine may be poking out. At this stage the collectors (mostly locals from a town called Al Nif) won’t have an idea what type it is. They are collected in bulk and taken back to the town where people in the fossil shops (Al Nif has 4 or 5 trilobite-based fossil shops, as they are found very close-by (we stumbled across one of the outcrops on our way out of town)) where one of the people there will prepare the ones they think are most promising using an air pen for the bulk rock removal and a pin or fine tipped air tool for the really fine stuff. Many will be damaged but can be fixed with glue (especially free-standing spines and looped spines than need preparation under them).
Most of the less decorative/impressive trilobites will usually fetch £10-30 depending on size and preservation, with the more spiney ones fetching anywhere between £50-£200 depending on how ridiculous they are. Prices like £1,000 on eBay and some sites are well overpriced almost all the time and not worth even looking at, don’t pay anything over £100 in my opinion if you’re looking to buy a Moroccan trilobite online. This one though is exceptional, probably somewhere in the region of £4/500 I’d guess.
Occasional fakes do occur, but I’m not really sure about the technicalities of these, and the ones I saw out there were all genuine. Slabs containing multiple trilo’s are incredibly rare so instances of these being sold are likely composites or even fakes.
The trilobites from these localities at Al-Nif rarely get over 15cm, although much older trilobites found elsewhere in the country can reach 70cm or so.