With the date jumping, i had the same problem when i used aftermarket date wheel on gen rolex. I then got gen datewheel and the problem fixed. I think it's about either how the teeth of the datewheel is cut or warperage of the datewheel... just a guess
the hand itself could become loose. this can be easily fixed by most watchmaker. Tightening itself can be done by tweezers, etc but you aren't going to get it right and you need a tool made for this.
it's just like buying stocks... without hard limit and discipline, you could spend far more than you should. Some items do get bid up crazy. Some other time, the listing is done poorly (title lacks details, etc) bc people who want it don't find the item, or the photo is so bad (but the real thing is actually nice) - in these cases, you can score nice items for good price.