Visiting your posts, you seem to have established a pretty interesting tie collection. What do you look for in your ties?
There are a number of criteria which lead me to buy ties. Aside from my bow ties, almost every tie I own is second-hand, so I'll address how I go about making my selections amongst a thrift's cacophonous cravat collection.
1. Design - If the design doesn't appeal to you, move on. Otherwise, pick up the tie. Before anything else, make sure the tie is long enough, that you've not picked up a boys' tie or a tie so old its dimensions are outdated.
2. Cleanliness and Composition - A number of wonderful ties are donated due to stains, rips, fraying, and so on. Examine every inch of the tie with your eyes, but also feel it for any problems not easily noticed under bad lighting (I do this because every thrift shop in my town is very poorly lit). If you haven't already figured out the composition by touch, check the tags. Stick to natural materials - silk, linen, wool, cotton. A good silk will be quite smooth and have nice weight to it. If you're not satisfied with the tie at this point, keep looking.
3. Maker's Labels - You can tell a great deal about the quality of a tie before you reach this step. In fact, this step may be superfluous for the experienced thrifter. However, if you're just beginning to build your collection and are not sure what to look for, consider country of origin (which you probably noticed while checking composition). If the tie was manufactured in America, Italy, England or Scotland, you've likely come across a quality piece. The last thing worth noting is brand. Countless tie manufacturers have come and gone. Don't be surprised to enjoy a tie from a company with which you're not familiar. Also, don't submit to the notion that because a particular company's production quality has dropped, all its pieces are inferior. This holds true for not just ties, but all clothing and accessories. For example, I have a number of vintage Chaps Ralph Lauren ties on par with any of my Polo ties. I also own a great deal of vintage Gant ties that far outweigh the make of the company's current pieces.