The only clothing swap I have been to I dropped of clothing (a bag full) and 4 pair of shoes the day before (drop of time was Noon - 5pm)... I got a voucher then saying I could take a bag full and up to 4 pairs of shoes. If you brought 4 bags, you got to take four bags. Also I know that they went through the bags and rejected any clothing that was well worn or stained, not fair to give unusable clothes but take usable clothes.
A true clothing swap is you give and take, you can not just take.
Ok now I remember what how the church I went to did this... if you gave something the above is followed and you then were allowed to come in from 9am-11am to get first picks (and could only take the same amount you gave)... from 11:30am - 1pm the clothes swap was opened up to the general for a small amount $5 to fill one bags of clothes/shoes, $10 to fill two bags (not allowed to fill more then two bags unless you actually gave more then two bags of clothes). All the proceeds went to the church's mom's group to put on more events or pay for any items bought to put on that event.
Time line as I remember it:
Drop off day before from Noon - 5pm
I noticed that ladies were already laying out the clothes during the drop off
Sure they set up past 5pm, but if setting up during drop off it will go quicker if there are helpers to do set up.
Next day 9am - 11am anyone who dropped off clothes came with voucher to have first pick.
Break just helpers can have a quick snack, use restrooms and maybe straighten the place up if a huge mess.
11:30am - 1:30pm open to the general public ($5 one bag, $10 two bags)
At the swap I went to at least half the moms that dropped off clothes did not participate, they just gave clothes so that is the only way it could be opened up to the public who did not give clothes. If you plan on doing a true swap you can still open in up to the public to do the swap but omit the last part the time for non-swappers paying for bags.
Hope that helps, I did not run it just was very aware of all the details because I was intrested in doing one... instead our church did a larger kids clothing & toys rummage sale which went really well. We provided tables and the space and both members and the genreal public were allowed to have tables to sell. Set up time was 7:30am-9:30am the rummage went from 10am-5pm. The mom's group at the church sold concessions (hot dogs, salads, cookies, veggie pack, whole fruit and various drinks), all the proceeds from this went to support more events put on by the mom's group and cover the cost to put this event on.