That's disgusting! It is dishonest and unethical for the purchaser to enter your model as his/her own build. Like most reputable contests, GSL rules prohibit entry of any model that was not the sole work/creation of the entrant.
From the GSL Rules:
"Section B. Model Eligibility, Classification and Presentation.
To better understand the rules of the GSL International Scale Vehicle Championship and to make sure that your entry(ies) will meet the qualifications for competition, please carefully review these eligibility and classification rules:
1. Model Eligibility/Individual Craftsmanship. The GSL Championship rewards and encourages individual craftsmanship and creativity. GSL rewards individual effort, not partnership, committee or "contract" construction of entries (except as noted in the BOXPLUS Class regarding models prepainted by the manufacturer). To be eligible for competition, each model must be constructed exclusively by the entrant. No one other than the builderentrant may: i) install any upholstery, materials or kits, ii) apply any finish/paint job/graphics design work (aftermarketpainted kits are not permitted in competition under any circumstances, and manufacturerpainted kits are eligible only for BoxPlus Class); iii) install any component preassembled by anyone other than the builder/entrant (such as a prewired distributor), or iv) do any assembly tasks."
While you cannot help what someone does with a model bought from you, the purchaser dishonestly stole that 2nd place award from a deserving entrant.
And, it is this kind of subversion of rules that can impune the integrity and jeopardize the reputation of a revered competition such as GSL.
The purchaser should be ashamed of himself/herself.