A lot depends on which dealer you are using, all will deduct for bad shot beasts saddle or haunch , some will class as saddled if the spine is broken anywhere along its length apart from the neck others only if fillets are damaged
you will loose quite a % for saddled or haunches carcasses and it's usually a good idea to salvage what you can from these and keep it for your own use.
The same with any where the bullet has burst the stomach , the bullet will carry stomach contents with it as it exits
contaminating the meat for some distance around that area, while its possible to use a hose to remove surface contamination it won't remove it from where it's been forced by the bullet, unless you can completely cut away the infected area back to clean uncontaminated meat it's best not to try and sell the carcasses is its likely to be condemned,again if you want to use it yourself that is up to you.
You can buy tags from BDS or the likes of Bushwear but most dealers have their own tags and will supply you with them if you are a regular supplier.
Delivered to dealer or collected from your premises heads and legs removed most will wan't the rib cage split and some the aitch bone split ask how they want the carcasses before supplying it prevents any confusion.
Your trained hunter number is the number on your DMQ certificate, some dealers will require you to sign a declaration some will wan't a photo copy of your level 1 certificate.
You will need to fill in the details on each tag that attach to a carcasse date killed species , sex and your signature
If collecting from you , your larder needs to be up to a certain standard , google supplying venison to an AGHE for relevant requirements.
It is also a legal requirement to keep a record of all carcasses supplied to a dealer , date killed, by whom killed,the
trained hunter who inspected the carcase if not the person who shot it, sex, a four figure grid reference(this is required for traceability in the case of serious disease) tag number, to whom sold and the date when sold, that is the basics required but you can add additional information if you so wish.
And finally while it's unlikely you will be chased for a couple of carcasses dealers also have to keep records of who supply's them so expect to pay tax on any income received if supplying on a regular basis.