講到這個我就有經驗，因為STEAM客服實在慢到有剩，又限制處理天數。
一開始跟你的狀況一樣，要我買禮物，然後我發現我要買的遊戲不能買成禮物。
然後就跟他一陣攻防，然後他回我＂抱歉，您的情況不能退費＂。
我就回去翻STEAM的規範，翻到以下這句：
https://support.steampowered.com/kb_article.php?ref=9950-QYJZ-0797
Once you understand the terms of this offer completely,
immediately purchase the correct version of this game.
If Steam blocks your purchase because you already own a copy of the game,
purchase the correct version as a gift and store it in your inventory
for later.
簡單講就是，買錯當下就去買正確的版本，
除非STEAM因為你已經購買過了不準你買，才去買禮物。
回他這句之後，他隔天就直接把$退到我的STEAM WALLET，也沒等我買正確版本。
(註：因為即將超過15天處理期限，STEAM回一次都需要2~3天。)
供您參考。
※ 引述《sidakong (Kevin)》之銘言：
: 前幾天特價時買了幾個遊戲，其中的Borderlands 2
: 因為破英文+沒注意看，本來是想買Borderlands 2 goty
: 結果買到Borderlands 1 goty+Borderlands 2
: 進遊戲缺東少西的才發現買錯了
: 只好寫信給Steam問看看能不能幫忙處理
: 等到回信如下：
: Thank you for contacting Steam Support.
: We apologize for the delay.
: Please purchase the intended game as a gift. Select the option "Store the gift in my inventory to send later".
: Please indicate when you have done so, and upon confirming your purchase on the account, I will cancel and refund your order for the original accidental purchase.
: To redeem this gift after the refund:
: -Place your cursor over your persona name at the top of the Steam interface, then click the 'Inventory' link.
: -Select the Steam tab. This will open the games/gifts that are currently in your Steam inventory.
: -Select the game that you would like to redeem onto your account. There should now be an 'Add to my game library...' button under the game's description.
: -Click 'Add to my game library...' to add the game to your Steam account. Once added the game cannot be removed from your account.
: Please note that if you originally purchased an item at a sale price and the sale has now ended, we cannot extend the previously discounted price for these items.
: This offer will only be valid for the next 15 days.
: 破英文看了一下
: 好像是說只要我把遊戲轉成禮物就可以幫我退掉
: 可是下面又有一堆步驟看無
: 看起來又不像是教我怎麼把遊戲轉禮物
: 所以想問一下是不是把遊戲轉成禮物再回信就可以退掉？
: 另外很少用steam，要怎麼把遊戲轉禮物呢？