How frequent is too frequent?

[1880nonsports]

met someone at a national 8-10 years ago. Shortly after meeting him he happened to post something in monthly pick-ups that would be the centerpiece of my collection. It was an item that really didn't "fit" in his collection (non-sport as opposed to BB) so I wrote him with a STRONG offer and he respectfully declined. I wrote him about 6 months later raising my offer and long story short - I wrote him and raised my offer once or twice for the next few years to around 10,000. (I'm no whale but I HAD to have it!). He answered me for a while then stopped responding - I figured he was tired of hearing from me. Fast forward couple more years and I manage to speak to someone at whose national table I had originally met the person, and he in turn was able speak to that person on my behalf. Apparently the owner who had turned down my 10,000. offer for an item (likely one of a kind) worth at least few thousand (?) at auction was robbed of his stuff including the display item I had to have...…
In another case I wrote someone 2/3 times about an item within a 6 month period. They always answered but declined. I stopped writing. Fast forward 3(!) years and they offered it to me at my price :-)