Hello and welcome !
Couple of things that might help would be upgrading your account to verified, u can do it here :
https://www.epicnpc.com/infocenter/upgrades.html
Its the first thing id do to gain anyone`s trust, gain that
verified status so they know u are legit and presented some sort of ID to the website.
This will be anyways
mandatory if the service u provide requires u to access the customers account, so with account share.
Another aspect, prepare a thread with a decent offer explaining the services as much as u can in detail, so the customer knows exactly what he/she is buying.
Put down your offer, price, payment method, contact basicaly anything the customer should know and be aware of.
Take a look at the forum rules when creating the thread, they can be found here :
https://www.epicnpc.com/infocenter/forumrules.html
If u wanna make your thread more visible, buy some credits and enhance your title with red/green colour from the store.
U will have a 6hrs cooldown before u can bump again your thread for free using the "bump" button.
If u think its not enough, u can always get some credits and get the "evade bump timer" feature to make sure ur up in the list more frequently.
These are some things u can do to make urself known around here, as for the reputation, dont worry about it, it will come.
Hope this helps mate, good luck with everything !