Not necessarily so in my experience. I've bought a couple of TT's off the classifieds section on PFM and AOS forums over the years, and in both instances the decks arrived superbly packed, bomb-proof in fact, and in pristine condition. Now Ebay could be a different kettle of fish.
If I had £300 i would be tempted to go for a brand new project carbon, the Ortfon red cartridge itself on that is worth £80
I did go second hand beacuse I was not want to spend a lot in case I didnt take to vinyl,.... got a technics SL1300 for £70 from the local loot paper, it needed slight attention, I had to resolder the phono lead connection as the left channel lost sound, and the 45 speed had issues with speed stability due to a dirty variable pot control , which can be sorted with some electical contact cleaner, but now it works great and sounds good with an AT95E cartridge, The SL1300 , 1500, 1900 etc can be had for a lot less than the SL1200 used, Not sure what the mechanical differnce is but they are apparantly the more domestic varations on the SL1200 so are more likely to not to have been thrashed , and they seem just as heavy and solid and have the same arm and platter, I love mine,
BTW i have taken to vinyl and ended up upgrading to an offboard phono, theSL1300 deck is staying until it dies completely if ever, I reckon i would have to spend many hundreds brand new to better it
going used has its risks, but bargains can be had too, as I found out