When you get a box of wooden planks directly from the lumberyard, they're arranged in the order in which they were cut. If hardwood floor installers lay down these planks right next to each other, you'll end up with uneven color variation, which won't look good once your entire floor is installed. When you call up prospective hardwood installation companies, ask if they mix planks. Also, make sure to ask them if they space out the planks when they install them; if they don't, the structural integrity of your floor won't be as good, and all of the seams on the planks will line up in an unsightly way.
During the colder months of the year, wooden floors contract slightly. While they might only contract about a quarter of an inch away from the wall, if your floors are installed during the winter and hardwood floor installers don't leave room for expansion, your floors could do damage to your walls when the warm months roll in. Experienced flooring installers won't make this mistake.
Many times these issues involve improper sealing or lack of a sealant between your new floor and the basement or crawlspace. Do they use a moisture meter? Ask about these issues and if they know how to address them.
If you truly want hardwood, you might have to get involved in the purchasing process.
Ask your hardwood floor installers for the contact information of prior customers to check up on their reputation. Also check online customer reviews.