When I was a kid I used to help out a hobby shop owner at shows and in his store. He was a major LGB importer and didn’t know too much about Lionel and American flyer. I was only a kid of say 11 or 12 but had a good under standing of Pre war post war trains so he took the standard and o-gauge trains in on trade for the LGB. Then he would sell it at shows on a separate set of tables. The owner would let me to run the o-gauge tables and I would head out to scope out the show before it opened and make some trades for items I thought would bring more attention to his table, sell faster/ better or at a higher price. He also would let me bring stuff of my own to the shows to sell/trade and put it on the tables.
I would take breaks through out the day and trade my wares for items I really wanted.
Bottom line was less trains on the table by the end of the show and money in his pockets.
I did that for quite a few years and I was proud of the fact that he trusted me to make good trades even though I was so young and it wasn’t my cash.
People would come and haggle for price at the tables and that was ok. Until they tried to brow beat him or I.
I remember one time we had a junk box under the table and every thing was marked for a dollar. There always was good stuff in it and you could get a working o-gauge switch with rusty rails to a tin 600 series freight cars with a wheel missing. The stuff was worth way more than a buck any way. One day this guy comes over and roots through the box and pulls out half the box to purchase. He then asked the owner could he do better on the price of the stuff (about 13 dollars or 13 items) to which the owner said sure give me ten bucks. He then asked if he could do any better to which the owner replied No that’s as low as he could go. The guy kept looking in the box and asking if he could do better a couple more times. By this time the owner was done with it but he didn’t say any thing and the guy finally left. About an hour before the show ended the guy comes back and looks through the box again and pulls out some more stuff, three tin o gauge cars missing parts and asks if the owner can do any better than 3 dollars for them all. The owner says sure 2.50 the guy looks back at him and asks again for a lower price because the show is almost over. The owner said no and the guy started telling him he was bad for the show and wouldn’t buy from him again or come back again .The owner very calmly said sorry that he felt that way and picked the box of junk trains up off the floor as some body else was just starting to look inside, he handed the other guy the box and said you can have whatever you want out of the box or you can take the whole box with you for free but only if you promise not to give that guy (he pointed to the upset guy) anything out of it and then put out his hand to shake with the other guy. Needless to say the first guy was very mad and started calling him some not so train show friendly words.
I think bartering and trading is good for shows but not so much for stores.
These are just my opinions.