HERE IS MY "DO" LIST
.1) .wash and wash (IF NEW) to get them softened.
.2) remove the stitching from the hems and steam them out. (good reason for buying larger sheets. You can cut trim at the stitching line)
.3) .check the measurements to determine if this will fit the quilt you ae planning. I find that Queen and King are preferrable inmany ways.
.4) used sheets are often nearly new. Check for 3 corner tears.
Overall...sheets someone else has washed will save you time, water and energy to dry them. Cheaper sheets could be coarse and not easy to hand quilt.
Lots of considerations, but worth thnking about.