In order to reply to the WTB thread and offer your service, you must have an active sales thread in #public-marketplace that is related to whatever WTB thread OP is looking for. Example:
Thread title - [WTB] 4G Proxies for Instagram accounts
In this case, you can reply to the thread and offer your services only if you are already a seller here with an active sales thread in #public-marketplace and you sell 4G Proxies. Posting a link to your thread is allowed so OP can check out your service/product and reviews. You are also allowed to message the OP too.
You are not allowed to reply in the thread if you have an active sales but you don’t sell 4G proxies.
All LVL1 (and higher) forum members are allowed to offer a service or product that OP is looking for, even if they don’t have an active sales thread, but only through Private Message (PM), without replying to the thread. Not even replies like “I’ve sent you PM” are allowed. Please note that you can only offer what OP is looking for, offering anything else will be considered as spam and you will be banned.