I've bough a ton of parts the last three years as I'm finally working on my '68 so here's my two cents. I'd rather pay a little more for higher quality parts but like everyone else don't want to be taken. Anymore I will shop several places for parts before buying. I've had good luck with Ames, Trim Parts and NPD - but watch NPD's quality. They sometimes trade low price for quality. I've had outstanding customer service from NPD, Trim Parts and Summit Racing. I try to buy in large enough chunks to avoid the shipping charges. Trim Parts quality is high but selection limited. Rick's Camaro was great for parts that crossed over to 'Birds before being purchased by Eckler's. Now their shipping charges are high. Inline tube has great quality parts but limited selection. For hardware, clips, etc. I check Inline first. Great quality, fair prices and fair shipping charges. They specialize in a lot of hard to find GTO parts. Like everything built by GM, there is a lot of part interchange. They have an outstanding Pontiac specific catalog. I've gotten a lot of bad quality OER repops and tend to avoid the brand. Summit and Jegs now carry more restoration parts and the shipping can be cheap by one has to watch. There is a local Chicago house, D&R Camaro, which I will check. He's a good guy. One can save money on freight costs for bigger items by buying local if possible. And you can see what you're buying before the purchase. And, don't let the name fool you, D&R carries Firebird parts too. I never bought much from Classic. Didn't want to pay the freight from California.
Buyer beware is what I've learned. FGF site is a great resource. Additionally, research the internet for part, distributor and/or manufacturer reviews. I've found some gems by doing so I would have never found otherwise. And avoided some trouble too.