Though I'm the first to acknowledge that automated appraisals at best have their limitations, in this case it looks like EstiBot is doing its job: Alerting you to a nice hand reg, a dotcom with nice keywords and the .net taken.
According to EstiBot rules, "a domain with a high valuation is at the very least worth a closer look". This is not one of the worst domains, and the $x,xxx valuation is designed to alert the user to that fact. It is not to be taken literally, but it should bring your eyes to the keyword data and IMO this domain is easily worth the reg fee, and more.
Here's the data
Domain : shirtstshirts.com (.com available, .net taken!)
Keywords (Autodetected) shirts tshirt
Frequency 133,000
Anchor Text 30,500
Title 19,500
Backlinks 0
Alexa Rank Not Ranked
Traffic (uniques) / Day N/A
PPC Ads Score 5.5/10
Related Searches/mo 167832
http://EstiBot.com BETA Valuation : USD 2,500
Not a wholly unrealistic price for an end user. Keyword data is reasonably strong and the domain is brandable: shirtsTshirts.com. Also, the .net is taken which increases the value somewhat, and puts this in that category of rare available dotcoms.
The PPC market for t shirts is pretty nice. This domain name brings up quite a few ads.
I would reg this personally. Then SEO + PPC ads, I'm pretty sure it will pay for its own renewal while you wait for the end user. Should see some type-ins.
Reseller I agree $xx, at least before any parking PPC data comes in.
Definitely not one of the worst hand regs.