Whether or not you need "good credit" to sell credit tradelines is a nuanced question:

You don't necessarily need an excellent overall credit score to be a tradeline seller. 

However, the specific credit card you are selling as a tradeline needs to have an excellent track record, with: 

• Spotless payment history: No late payments, defaults, or collections on that specific card.

• Low utilization: Ideally below 10% and maintained at a low level throughout the authorized user's tenure. 

Why this matters:

The value of the tradeline to the buyer lies in its positive impact on their credit report. If the tradeline you're selling has a history of missed payments or high balances, it won't benefit the authorized user's credit score and is unlikely to be accepted by reputable tradeline companies. 

Essentially, while your personal credit profile might have some blemishes, you can still be a successful tradeline seller if you have a few credit cards that you have managed impeccably over a long period.