I like the combined suggestions of three other commenters:

1) Allow transfers during a very short window (e.g. 24h before the event)

2) Allow full refunds up to x days before the event

3) Release a small batch of tickets 24h before the event, as a way of reducing the chance for scalpers to make money, and giving real fans a last chance without paying exorbitant prices

All three together offer a reasonable tradeoff. The tickets will go (mostly) to real fans, yet still giving you flexibility in case your plans change (work, sick, etc). And if you know well in advance, you can get a full refund, without having to worry with reselling, paying commission, etc.

Also prohibit secondary markets entirely. Similar to airlines, there's no reselling of tickets.

Of course, this is just wishful thinking. Too many intermediaries benefit from screwing showgoers, so this will never be implemented.

For most popular events there are enough people who want or need to make plans more than 24h in advance that scalping would still be profitable.