So if you want to participate in this thread, our objective is to: identify, validate, and generate ideas regarding the process. It'll be interesting to hear your experiences.
Here's a list of problems I've identified from older threads which have touched on this topic. Hopefully we can get a decent brainstorm going about this.
1. You can't take the swatchbook with you. Resultantly, your time of choice is limited to the time you spend in the shop. Some of us may feel under pressure by this unfavorable situation.
2. You can't always bring a swatch home. This occurs frequently.
3. The swatch is too small. Resultantly, your choice is a crapshoot until you get to see the big picture.
4. The desired fabric or brand is not stocked by the tailor or distributor.
5. On the internet, fabric colors are inaccurate because of lighting, the monitor, and camera lens.
6. On the internet, fabric quality is underappreciated due to a lack of high resolution photography. This occurs frequently.
I hope you can continue the list, or validate what I have already posted. Have fun!