Hello there,
This auction was handled poorly since it doesn't fit with our Trade Rules.
12. In auctions, the auctioneer should respect PRO's Auction Rules, using Auction Template, announcing the item(s)/pokemon(s) being auctioned, call and acknowledge bids made, and announce the winner, said rules should be respected.
AUCTION RULES:
Due to the latest Trade rule #12 revamp, all auctions shall have the same rules and respect PRO Trade rules. Auctions cannot be cancelled once started and as counter-measure for sniping, if the auction receives a bid during the last 15 minutes, the ending point is delayed to +15 minutes from that bid, until someone being the c.o. for 15 minutes wins.
Here when you received an offer before the 15 last minutes ended you simply continued the current time and did not start anew with the 15 minutes as the rule state.
The time stamps of your message and the time you set for your auction end differs.
Also as to answer your question, the minimum bid raise is only optional but it can't be changed once set.
Be sure to follow the Auction Guide for your future auctions so that this won't happen again.
Best regards,
Rayjuu.