The issue of 'contractors' selling collections is not one I have suggested is likely to happen. They are, as John has said, temporary custodians in every possible sense. In Gloucester we required (it may have changed) as part of the brief and contract, that the correct disposal of finds and archives should form a part of the planning approval. The need for this to be agreed in advance of fieldwork is, in my view, paramount. I know of at least one site where a single find group if sold on the market would have more than paid for the developer's costs - if the ownership of the portable antiquities had not been written into the process.
The use of volunteers for cataloguing is common enough in museums, but the results are only as good as the volunteers' abilities and experience, so there are risks. I recall discarding a jet bangle in a site search when I was at school, because I thought it was plastic - fortunately someone else recognised it and rectified my error, but even then I was very familiar with archaological material. Some volunteers are excellent - others less so. It is a strand to a solution, but not the only one.
Rather more alarming (but not new) is the lack of interest in collection studies by university students. This at least in part must refelect the views and prejudices of the tutors. lecturers and staff who themsleves are uninterested or ignorant.
Artifact studies are difficult and rarely reach a solid conclusion. I have been researching the Gloucester Tables Set for well over 25 years, and still find new information. I have been seriously studying for five years the (not archaeology as we would know it Bones) products and story of Roberts Borthers of Gloucester who only closed in 1956, but the main techniques are typological, and rely on the accident of knowing that products both exist and are Roberts - all of which is a constantly changing situation.
Sadly, the best source of research on collections is the local museum curator who beavers away quietly for year after year, but these people are increasingly unlikely to exist. Curators in archaeology are an endangered species (how many exist in the Hub museum at Bristol, for example) who are likely to go the way of curators in geology and natural history. They are being swept aside because the popular view of the disciplines is more 'out there' whether it be chasing furry animals around the countryside or digging important heritage in a three-day blitz or being startstruck by a hoard of Anglo-Saxon bullion.
In that competition, the discovery that a bottle may have belonged to an identified local bigwif during the ECW seems fairly small beer, while the recognition of the extent of trade with a town isdull, dull, dull.