I've purchased several items, all pleasant transactions. I've also said "yes, I'll buy," but had to retract. In one case I was going to buy a flash and sent the PM, but the next day the same flash with all accessories was listed so I went with that. In another case I was going to buy a Zeiss Ikon when a M6 TTL was listed for a few $$ more. I went for the M6 😀 Lastly, I almost bought a Jupiter 35mm, but when I found out that there is problems when using the in camera TTL metering, I went with the Ultron 35mm. I did sent a apology though in every case describing why I did not follow through with my transaction.
As for selling, I listed items once and had them up for a week. Only one person replied, half interested, so I listed on the EvilBAY and sold for a little more/less (multiple items) than on my RFF add. Next week or two, I saw a similar item as mine go for more that my original RFF price. I guess it's all about the timing.