be careful when purchasing used blades in lots, often times groomers will save up all their old burnt out blades, then sell them in lots, by burnt out i mean there is nothing left to sharpen, there is only so much metal on a blade to sharpen, i have purchased many lots of used blades[detachable blades] out of the lots of 10 or more blades i have purchased i was only able to sharpen 3 to 4 blades. not only was the blade worn down but many were missharpened along the way and they never cut right. to sharpen a blade that has been missharpened in the past, the sharpener must remove twice to three times the amount of metal to bring them back to a cutting status, i have seen ebayers bid up to $100.00 for 15 used blades, you could purchase 7 new blades for that price if you shop around, don't get burnt any more, shop around and buy new or bid low on used blades.every groomer should own a compressor to clean the blades, keep your blades dry after use, or keep in a good blade wash. when you store blades away for a time, make sure you clean and dry all the parts of the blade, that is where the compressor comes in handy, then oil all parts of the blades, wrap in news paper and store in a dry location. you really don't want your blades to get rusty, if you have rusty blades, most of the time they can be sharpened, but more metal must be taken off to get them to cut properly, you cut down the life of the blade, if you take care of your blades, they will last years. when you send blades out to be sharpened make sure the sharpener has a reputation for doing blades right, even a new blade can be destroyed by a sharpener the first time around, find a sharpener that specilizes in only blades. don't always look for the cheapest sharpener, cheaper is not always better when it comes to clipper blades and scissors. in my earlier years of sharpening, (many years ago) i destroyed quite a few blades, i did learn my lesson and so did a few of my customers, stay away from the do it yourself sharpeners, i'm talking about the round disk sharpeners. waist of money. the round disk sharpener will not hollow grind or hone the top cutter, the top cutter must be hollow ground on all detachable blades,,send your blades out to be sharpened by some one that specalizes in blades, do not over oil blades when you are grooming, the blades will cut much better when lightly oiled, to much oil will lift the top cutter, kind of when you go through a puddle of water with your car, i had a guy call me up and tell me his blades were not cutting, he said he had oiled the blades good, i told him to clean off the exess oil and try again, he did, he emailed me back and said (it worked) make sure the two screws are tight. the screws are what keep the spring pressure on. you can have super sharp blades but if you dont have enough spring pressure your blades wont cut, just like scissors, groomers send scissors out to be sharpened, first thing they do is loosen the screw so the blades are loose. what happens when you do that is you will be grinding the blades together and destroying the sharp edge that was put on, your scissors wont last as long. barbers are noted to loosen screws also for a relaxed feel. if you want a relaxed feel from a pair of scissors, purchase a better pair, convex scissors are much smoother than non convex.by convex i mean the inside of the blades are not flat but have a ( to them. only the very top of the blade is making contact with the other blade. hope all this helped you out.  i flunked english in high school, please cut me a little slack. bob