I do regret not purchasing more pipes at flea markets when I went to europe last year(still kicking myself for the gbd silver band one!). They were in a abundance everywhere for less than 20$. I bought maybe 20 or so but should have just filled my luggage with them haha. Most were for refurbish and resale, but I've kept some that I like and maybe tripled my investment.
I had a nice old stanwell author that I let go for too cheap and really liked, it was the most comfortable pipe to clench(really for the authors!)
Missed out on a huge lot of clays for cheap I could have sold.
Oh well with all my pipe refurbishing and selling I've basically paid for all my pipes and made a profit and I currently have more than enough pipes(briar, clay, meerschaum, cob) for myself (20 or so). There's always more cobs if I get some PAD, I only have one and maybe I'll get another at some point. So yes some regrets, but I love the ones I smoke and get all the enjoyment I need from them, so all good.