My shul sells tickets for High Holiday seating. These are paid specific seats for the person who reserved them.
Sometimes, outsiders attend the shul on Rosh Hashanna. Our shul doesn't refuse them entry, and, most likely, doesn't check where these people sit. Most of them haven't paid for tickets either b/c they don't know the rules or b/c they can't afford it. So they sit in any empty seat that they can find.
Is there anything halachically wrong with someone sitting in these paid seats before the payee arrives? Is the seat considered the payees "property" even if he never shows up, or does he own it only from the time that he attends the shul? Does it matter if the payee stipulates in advance that no one should sit in his seat at all? (I know that may sound strange, but in my shul, some people are overly sensitive about this. They really don't want anyone ever sitting there even if they don't show up!)
My question is most applicable to Rosh Hashanna / Yom Kippur, but could apply to any time of the year, as well, such as a (un)paid makom kavu'ah.