Well any tightlacer worth her salt has probably tried to buy a corset on ebay...no doubt half of them have been dissapointed by items that were listed as "corsets" but are really plastic boned bodices! here are a few tips that have helped me when searching for the real deal!
Always put "steel boned" in your search keywords, this way most of the items that come up will be in the right ball park. Always check with the seller (if not stated in the listing) that the corset uses flat steels at the back on either side of the grommets and either side of the busk, or front if no fastening. These are what help you to tightlace and give firm support to control the tum and improve your posture. The flat steels at the back also help to keep the shape at the back taught whilst laced up, and increase the life of your grommets by taking most of the strain.
If a corset is to last a long time it should not use standard eyelets! Grommets are very similar to eyelets but they have a "washer" over the back that makes them last longer and also protects the fabric, as with a lot of pressure, eyelets can tear their way through the fabric. Gutting when youre in the middle of a night out!
Whilst many traditional corsets, built by the victorians themselves were made of one layer, this would almost always have been coutil (see below for explanation) to be strong enough for regular wear. The more layers, the better the corset will look, 4-6 is an optimum number. The corsetry canvas that i use in mine smoothes down the figure so you dont get that pulled-taught and bunched look from flimsier corsets, or bulges from tightlacing! This can also make for a more comfortable wear as youre less aware of individual pressure from the bones.
Off the rack corsets are all very well when youre in a rush but dress sizes really dont apply to corsetry! you need precise measurements at bust, waist and hips, if these are not included in the listing, then ask! knowing the waist size alone is not enough, as a surprising number of us are different sizes at bust and hips. This is especially true with corsets as your waist size will be smaller than normal, and if its gaping at the top and bottom, it not only looks ridiculous but is also uncomfortable to wear! A good gap to have is a nice even 2". This isnt always possible but its a good thing to aim for!
Made to measure items are naturally going to give you a better fit, but of course this is a little worrying to deal with through ebay and online. A sellers feedback is a good way to judge the quality of their work (i know that sounds obvious!) ask loads of questions and make sure they are clear about every part of your order before finalising. Do try and remember that corsets are very complicated items and sometimes things do go wrong, if you are unfortunate enough for this to happen to you then stay patient and a good seller will always work to fix your problem.
Coutil-This is a traditional corsetry fabric, it is very dense, thick and usually cotton based to give a breathable but stretch free material. it can come in some stunning colours and designs but is very pricey and hard to find, so this will be reflected in the price!
Steel boning- This has replaced the original "baleen" or whalebone for ethical reasons, spiral wire, which is used on the majority of the seams for flexibility, also makes the corset more wearable and healthier for the wearer. Only corsets which use flat steels AND spiral wire are suitable for tighlacing. Some underbusts can also use only flat steels but spiral wire should never be used alone in real corsets.
Plastic boning -This is what youd expect to find in a "bustiere" from new look. It snaps readily and the sharp ends will work their way through the fabric to poke you in inappropriate ways! It also heats up and molds to your figure, so it will not do anything for your figure other than cling to it.
Lacing- Some cheaper manufacturers will use shoelaces to tie their corsets up at the back, but these arent really right for the job. Real corsetry lacing is available, it is designed to have no stretch so you stay where youre put!