It's great you're getting solid advice already from the members here. I strongly agree with testing everything live! A few sticky keys are normal but if an entire bank of keys feels sluggish, pass it on! Aside from checking the keys, carriage, and platen, also check that the margin bell dings and the ribbon spools turn. I'd also say the biggest mechanical killer is a broken drawband. Curious to know what models are you leaning towards?I'm new to typewriters and want to buy a used one. What should I look for, and what common problems could I run into before I buy?