Tips for buying used Vinyl needed

I see there is a learning curve to buying used vinyl, can you please offer your wisdom and experience? In my recent attempts at buying used vinyl I have learned not to buy from someone who has stored their collection in the garage, dusty, moldy, and urine smells are gnarly. I am starting to look closer now that I have brought some home from my local shop and noticed imperfections in the vinyl itself, resulting in pops. Finding thirty and forty year old records in good condition is not as easy as I thought it would be.