What should I look for when purchasing a quality album?

Buy what you like to hear. Do buy used LPs but only under the following stipulations: (1) you examine the LP yourself, both sides, and there are no, zero, scratches or blemishes, and the surface retains its new vinyl sheen, or (2) you buy from a reputable source on line that grades their used LPs, and you buy only Grade A, or (3) you’ve grown to trust a vinyl reseller and he offers right of return if the LP is unlistenable. You almost have to be willing to buy used LPs if you want to accumulate a decently large collection, and if you are starting from scratch, unless you are wealthy and/or careless about the amount you spend.

There are dependable quality labels, but any attempt to list those will inevitably be incomplete. In jazz, I can recommend in no particular order ECM, Steeplechase, Pablo, Verve, Columbia, some Capitol, Vanguard, Pacific Jazz (old label, mostly mono), Riverside, Contemporary, Atlantic (somewhat colored but will produced), Blue Note (to me also somewhat colored but very collectible and therefore sometimes ridiculously pricey), Jasmine (which seems to be reissues but good sound), MCA,..... I’ll stop there. Someone will recommend Direct to Disc labels. Yes, great SQ but the artists on those labels are seldom first rate.

I use Music Direct if want a new album. Typically buying only audiophile pressings. I have had very bad luck with Amazon. 

If I want used, I go to a local store so I can examine the record carefully. 

The cheapest option is to buy bulk. Estate sales, shopgoodwill are fun ways to find albums. You’d spend 30 bucks for 10 or so albums, and some will sure be good quality. Used record stores are the second best option. All my favorite and best sounding records cost less than $10.

There are labels I avoid and some that I trust but it might be subjective. CBS, Decca, Columbia, Atlantic, PolyGram, Jet are all decent

Don't discount Craigslist, either. Snagged some good ones off of there.

Also had good luck on eBay for harder to find ones. Just check the sellers feedback and what he rates the album.

grislybutter and thecarpathian are willing to buy LPs in bunches at low per issue cost and apparently are prepared to find many of such LPs to be utterly unplayable. That’s another valid approach, I guess. I once spent an entire afternoon looking at LPs in a Goodwill. Some had no inner sleeve (a very bad sign because the cardboard cover will itself damage the playing surface), many more had outright gouges in the playing surface, gross dirt, etc. I guess those guys have more patience than I but I would rather pay $5 (for mono) to $15 for a single LP that passes the eye test and contains music I know I want to hear than to pay the same amount of money for several miscellaneous LPs among which I will be lucky to find a single gem. I don’t do estate sales unless I know the guy who died to have been a fastidious collector. Nor do I do eBay unless I have confidence in the seller. Thrift stores like Goodwill.... Stay away. But that is just my opinion. We have one son who lives in Tokyo. Tokyo has superb used LP stores, and the Japanese apparently take amazing care of their LPs. Funnily also, the prices are highest on US pressed originals, compared to Japanese reissues of say Verve, Polydor, etc. Yet the Japanese reissues are often superior to the originals or at least as good. The store I go to once a year rates each LP on an A, B, C scale. Even the B-rated LPs are in superb condition. I don’t even bother to inspect their A rated used LPs, because I know they will be perfect. They also dramatically devalue mono LPs, many of which I find to sound wonderful.